world news with diane sawyer will come up next. >> thank you for watch we appreciate your time. see tonight on "world news," breaking news. bin laden plot revealed. what the u.s. found in the terrorist's compound. and strange new details about daily life, how he spent years in just two rooms with three wives. warrior dogs. the powerhouse four-legged weapons fighting alongside the navy s.e.a.l.s. gas prices. relief ahead? what happened today that could mean a drop in the price at the pump by memorial day. and living tree. the president pays tribute. and one pear tree at ground zero stands as a symbol of renewal for a nation. good evening.

it did not take long at all. the documents from osama bin laden's compound have already given up a vital piece of information. that al qaeda was plotting to strike america again, this coming september, on the tenth anniversary of 9/11. and the target? trains. our pierre thomas has been told about the details that prompted intelligence officials to issue a new alert today. and he brings them to us tonight. pierre? >> reporter: diane, investigators have been going through this evidence nonstop. and the initial sifting of this material reveals that handwritten notes about plans to derail trains in the u.s. authorities in all 50 states are being warned that al qaeda had been planning to attack train lines, potentially killing hundreds, on the upcoming anniversary of 9/11. the bulletin obtained by abc news states, "as of february 2010, al qaeda was allegedly contemplating conducting an operation against trains in an unspecified location in the united states on the tenth

anniversary of september 11th, 2001. as one option, al qaeda was looking into trying to tip a train by tampering with the rails so that the train would fall off the track in either a valley or bridge." >> you can't guard hundreds of miles of track. and if they can get to one location that's not well guarded and put explosives on it or do something to cause the train to derail, that's a lot easier than going after an aircraft. >> reporter: abc news has learned the bulletin arises out of evidence recovered from bin laden's compound, revealing that al qaeda remained fixated on so-called soft targets like transportation. this appears to confirm that bin laden still had a role in approving al qaeda plots, just as he did for 9/11, in which he openly bragged about his direct involvement in planning this that massacre. >> translator: i was thinking that the fire from the gas and the plane would melt the iron structure of the building and collapse the area where the plane hit and all the floors above it only. this is all we hoped for. >> reporter: one official tells

abc news the materials found at the hideout include schematics and websites involving a variety of things al qaeda was considering. one official describes the documents as aspirational. but not indicative of final stage planning. but the new evidence shows that al qaeda was planning attacks that echoed past assaults on commuter trains in madrid and london. tonight, throughout the united states, railroad and transit systems are ramping up security in response. and diane, this is only the beginning. it's the first read of a trove of materials that they're just beginning to review. >> as we said, it didn't take long. thank you, pierre. and we are also learning those strange new details about daily life inside that compound. and the true identities of the women who were there when bin laden was taken down. it seems they were not one wife and two strangers as we thought, but instead, all three, his wives. jim sciutto reports from pakistan. >> reporter: we knew that one of osama bin laden's wives was captured in the deadly raid.

29-year-old yemeni amal ahmed abdul fatah. but tonight, abc news has learned a total of three of his wives were taken. all of them had been living together with bin laden inside the compound where he was killed. abdul fatah has told investigators that for the past five years, bin laden confined himself to just two rooms, including the bedroom where he was shot dead sunday, with abdul fatah, who was injured in the raid, at his side. >> two rooms on one of the floor. he never went anywhere. >> reporter: tonight, held under guard in islamabad, the three wives are being interrogated, likely facing a firm but nonviolent questioning. >> we give them a questionnaire, there are 20 questions. she answers, then we change the order of those questions another day. >> reporter: investigators then look for any contradictions in their answers. >> they have a very, very good

memory. you find out, normally would tell you for the first day, the correct things. >> reporter: still reeling from being kept in the dark about the raid, today, pakistani officials warned the u.s. never to do the same again. and head of the pakistani military ordered the number of u.s. military personnel in pakistan reduced to, quote, the minimum essential. all week, u.s. officials have been pressing for access to those wives, but relations as bad as they are, pakistan hasn't granted it. as for the compound, pakistani authorities want to tear it down to remove any danger, diane, of it becoming a shrine to bin laden. >> all right, thank you, jim, reporting from pakistan tonight. and we did learn something new today about the picture that fascinated so many of us. the president and his team, in the situation room, watching real time information as the navy s.e.a.l.s took down bin laden. and secretary of state hillary clinton with her hand to her face. well, today, secretary clinton talked about that very moment.

>> those were 38 of the most intense minutes. i have no idea what any of us were looking at at that particular millisecond when the picture was taken. i'm somewhat sheepishly concerned that it was my preventing one of my early spring allergic coughs, so it may have no great meaning whatsoever. >> allergy or not, it did seem to express what we can all imagine feeling. and, today, president obama made his first visit to ground zero since taking office. for a solemn and silent tribute. he met today with 9/11 families, firefighters, first responders. and jake tapper traveled with him and reports from ground zero tonight. >> reporter: accompanied by a brooklyn firefighter who rushed to the world trade center that horrific day, president obama today placed a wreath at ground zero. taking a moment of silence in the shade of the survivor's

tree. at the president's request, also present were the widow and daughters of glen james wall, an executive at cantor fitzgerald. 14-year-old payton wrote the president about how she has handled the loss of her father. from staten island, came the widow and son of brian cannizzaro, last seen from evacuating workers from the south tower lobby. jackie says the death of bin laden brings closure. >> i feel that justice has been done. you know, he destroyed many lives that day and i just, i feel grateful that this has been done. >> reporter: christopher was only 10 months old that day. he said today he could see the world has not forgotten his father, because the president came here. >> he was talking to me about my necklace and what happened on 9/11 and what's happening here today and why he was here. he actually gave me a fist bump. it meant a lot to me. >> reporter: you want to be a

firefighter? >> not really. >> i think that's because i'm too afraid. >> reporter: many survivors say sometimes it feels as though those remains are still smoldering, as if a decade had not passed. >> i can hear you, the rest of the world hears you, and the people -- and the people who knocked these buildings down will hear all of us soon. >> reporter: it's taken a long time for the site to recover. most of the progress, just in the two years since then senator obama was here last. with the rise of world trade center buildings one and four and the foundation for much of the 9/11 memorial to open this fall. this is what the site should look like when building is completed. the president also spoke to firefighters at midtown engine 54 ladder 4 battalion 9. where he said the mission sunday was done in the name of the is 15 brothers they lost. >> when we say we will never forget, we mean what we say.

>> reporter: and diane, tomorrow, president obama heads to ft. campbell, kentucky, where he will personally thank some of the navy s.e.a.l.s and other participants in that mission to kill bin laden. dian diane? >> all right, jake. what a meeting that will be. and in a moment right here on "world news," we may have a revelation about who will be in that room. a four-footed warrior. s.e.a.l. team six apparently included a dog trained to help take down osama bin laden. more on that in a moment. but we move now to the news that millions of americans have been waiting for month after month. skyrocketing gas prices, finally heading down. today, oil prices took a plunge, below $100 a barrel. does this signal that the gas prices are soon to follow? how soon? matt gutman in miami tonight. >> reporter: today, all-time highs in four states, and 24 other states are within pennies of their records. hawaii still has the nation's

most expensive gas, but the nation's heartland is catching up. >> these prices are crazy. i'm putting $20 in here and by the time i get home it will be gone. >> reporter: but we learned today, the national average may have peaked, short of the $4 mark. oil and gasoline futures collapsed today. crude oil tumbled nearly 9% to less than $100. its lowest price in almost two months. gasoline futures, which help determine the price at the pump, down 23 cents just today. >> i am hopeful that in average places, prices will drop as much as 20 cents here in the next seven to ten days. >> reporter: so why the dramatic drop? it's partly due to sagging demand. americans are already driving less. a strengthening dollar has dragged down oil prices, as does poor economic news like higher than expected jobless claims. still, don't expect to get back to two buck gas like we had in 2009 any time soon. >> $3.50 a gallon price is going to be seen as relatively cheap over the next couple of years.

>> reporter: so far, rural areas have been hit hardest. check out pictures of these gas stations, taken today in alaska. yeah, that one reads $6.73. and believe it or not, there's one place where americans are seeing $9 gas, even today. the rental car counter. >> we have a fuel and service charge $9.29 per gallon. >> reporter: $9.29 per gallon. rental car companies say it's meant as a penalty, but to most, it just seems punitive. >> it sounds a little bit like price gouging, yeah, it does. >> reporter: and diane, check out the prices at this station. $4.19 for a gallon of unleaded. survey just out today found that americans spend about $390 in the month of april for gas alone. for many people, that's more than the cost of their monthly car payment. diane? >> still great to hear that could be changing in the weeks ahead. thank you, matt. and from illinois to louisiana tonight, the threat of severe flooding from the mississippi river is growing.

in fact, records that have held since the great depression have been broken. in memphis, we watched the disaster unfolding today. and we found a man who struggled to evacuate, his words said it all. >> you live with it. you live with it. >> so tough for so many people. and still ahead on "world news," as we said, a four-legged lethal weapon with the navy s.e.a.l.s, able to jump out of airplanes, even bite through kevlar vests. and president reagan's secret stash of wisdom, scribbled on his index cards. and why is a tree, once broken in the 9/11 rubble, a reminder today to look up at the sky? did you know prilosec otc can stop frequent heartburn before it begins?

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>> reporter: diane, we've seen them protect us, sniff out danger for us. in fact, hero works the train stations in manhattan. and one of his brethren in the military may have helped kill osama bin laden, the most wanted terrorist in the world. they do remarkable things. parachuting out of military aircraft with and without their partners. super dogs. and now abc news has confirmed that among the 24 super secret navy s.e.a.l. commandos team who swept into northern pakistan and killed osama bin laden, was one super secret four-legged warrior. this war dog at the training center at lackland air force base outside san antonio is one of nearly 3,000 four-legged warriors trained by the military. but a handful of those 3,000 are even more special. and just like the human special forces teams they join, details about the breed, the specific role or names of these super dogs are not being disclosed.

>> no, sir, i cannot. i don't know where those dogs came from. >> reporter: here is what we do know. this year, special operations command in tampa solicited private contractors to train 80 to 100 students and 70 to 100 canines per year. to among other duties, pursue, track, patrol and bite/hold fleeing subjects. >> a lot of it is under wraps and undercover. >> reporter: these super dogs must be the best of the best and used on this type of mission to both find explosives and help subdue targets. >> the dog has -- is an attack dog, trained to attack on command in addition to any bomb sniffing training the dog would have. >> reporter: the pentagon bought special gear for these special forces dogs, like these goggles. they're also equipped with waterproof body armor, resistant to bullets, shrapnel and knife attack. they are rumored to have the teeth they break during bite training replaced with titanium canines.

their jaws pack 400 to 700 pounds of pressure. quite a bite. the super dogs are outfitted with head-mounted infrared live cameras, allowing handlers to see what they see. and ear bugs so they can be given remote orders. the trainers say the most valuable part of the war dog is its heart. >> your relationship is your best friend, your partner. your life and the life of the soldiers that you're supporting depends on him. if you don't know your dog and you don't trust your dog, it cannot only mean your life, but the lives of the people around you. >> reporter: and while these war dogs do get wounded and even killed in battle, they are not eligible for any kind of awards. and as far as those teeth, they can bite through kevlar, but they are not any longer replaced with titanium, we're told. diane? >> all right, thank you jim. ear bugs in order to get remote orders. that is a wow. we salute them. coming up, president ronald reagan's secret note cards. the words he lived by.

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history had called this generation of americans to be watchmen on the walls of world freedom. he liked to laugh, president lincoln. he said, if i couldn't laugh, i couldn't stand this job for 15 minutes. one of my favorite quotations about age comes from thomas jefferson. he said that we should never judge a president by his age. only by his work. and ever since he told me that, i've stopped worrying. >> he apparently kept the notebook in his desk, and after his death, it was boxed away, only rediscovered in this past year. and, the last known combat veteran of world war i, anywhere, has died. claude choules was born in a small town in britain. he started training with the navy a month after turning 14, didn't tell them his real age. he never lost his love of the water. he swam in the sea until he turned 100. claude choules was 110 years old. and, coming up, one tree's

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gout flares, joint pain, and rash. [ male announcer ] if you have gout, ask your doctor about uloric. and finally tonight, ten years ago, a small pear tree, charred and mangled, somehow managed to cling by its roots to the earth beneath ground zero. well, today, that tree received a president. and here's john donvan. >> reporter: that silhouette rearing up from the ashes nine years and seven months ago -- the eye went straight to it -- unwillingly. an accidental grave marker, standing for death. suggesting defeat.

but it's gone. long gone. so today, the focal point, in a moment of victory, was a tree. something that is alive. and that's not to be taken for granted. for this tree, on the morning that the buildings came down, it was in the path of the collapse and buried in the wreckage. and when finally uncovered, it was naked, nearly limbless and barely alive. it was the city's parks department that set out to save it, which meant getting it to a safe place. a nursery in the bronx, for, literally, some nursing. and it worked. around the blackened scars that were burned in on 9/11, new healthier bark grew in. and branches sprouted and those branches branched. a setback last winter. still in the nursery, a storm rocked the tree, nearly onto its side. the flag that kept it company went over, too. but they righted it and they fed it and late last year, they brought it home. the survivor tree, it was now called. joining a little orchard the

city had decided to put in at ground zero to bring it back to life. only the survivor tree had been there before. and will be there to feel the seasons for a long time to come. john donvan, abc news. >> and we thank you for watching. we are always on at abcnews.com. don't forget, "nightline" later. and, we will leave you with live pictures, tonight, from ground zero, where that pear tree is standing strong. rl >> tonight california's two billion tax wind fall. how far will it go to ending the biggest budget crisis in history. and the a tourust in san francisco last year. why the suspects in her murder claim that police botched the case. >> pidge wins the round to

install the smart meter. the rate increase that requires you to help pay for them. >> ahead on senon - 7 on your side. i am michael finny. one family's two year battle to keep their home out of foreclosure. >> good evening, state lawmakers may not need as much as your money. >> unexpected surge of tax money came in and it could take a bite out of the budget. >> annette miranda is live in sacramento reporting on the money tonight. and since january, it is a continuing in a strong clip. corporate taxes are up and more money are working. >> an unexpected two and half billion surge in income and taxes have lawmakers hoping that it is a sign that the finances are improving.