save. get ten dollars off with no exclusions! we make style affordable, you make it yours! jcpenney. tonight on "nightline," reversal of fortune? a startling new development in the case of amanda knox, the american student convicted of murder in italy. on the eve of a critical hearing, there's explosive new revelations that could set her free. is this the breakthrough her family's been praying for? role of a lifetime. from "white castle" -- >> what's going on up there? >> -- to the white house. for the first time, actor kal penn opens up about his unlikely career in politics and his return to hollywood. and debt for dummies. we have the latest on the political wrestling match over the nation's maxed-out credit line. how did we get here and can these guys possibly make it any worse? we have the crisis by the

numbers. good evening. i'm bill weir. there is news tonight from washington, but none of it good. republicans jammed a revised debt limit plan through the house tonight, but it was swiftly killed by the democrats in the senate with little sign of the parties coming together, a stalemate continues as does the relentless countdown towards tuesday's default deadline. we'll have more on the crisis later in the show. but first, a stunning new revelation that could spell freedom for imprisoned american college student amanda knox, convicted of murder in italy. elizabeth vargas brings us the very latest from perugia in our ongoing series "crime and punishment." >> reporter: it is a journey amanda k kx's mother, edda mellas, knows too well.

>> i have lost count of how many times i've had to travel. >> reporter: shuttling back and forth, 6,000 miles between seattle and italy, to visit her daughter in the foreign prison she has called home for 3 1/2 years. but this week's visit was different. for the first time knox was brimming with hope after a drastic turn of events in her epic legal drama. >> she talked about how w od a day it was. she did talk about things she wants to do when she gets out. so i think that's a positive sign. >> reporter: in 2007 knox was transformed overnight from a fresh-faced student into an international murder suspect after her arrest in the gruesome stabbing of her british roommate, meredith kercher. the tabloids labeled her foxy knoxy. >> [ speaking foreign language ]. >> reporter: during the trial the prosecutor had no eyewitnesses and no clear motive. >> [ speaking foreign language ]. >> reporter: the case rested entirely on two pieces of evidence. first, a knife found at the apartment of raffaele sollecito,

knox's then boyfriend, also on trial. the prosecution claimed it was the murder weapon, saying the knife had knox's dna on the handle and kercher's dna on the blade. second, kercher's'sra clasp, found in the bedroom where she was murdered, had sollecito's dna on it. according to prosecutors, it was enough to convict them. knox was sentenced to 26 years in prison and sollecito to 25. after the verdict knox's family, stunned and angry, fought their way through a mob of press and local perugians. >> how do you think this whole experience has changed your daughter? >> she was 20 when she walked in here. she was naive, happy, lovely. she's way more cautious. she had to xwroe up, you know, really fast. >> learn some life lessons. >> huge lessons.

>> reporter: this week knox was back in court for her appeal, looking fragile and pale. prison life has clearly taken its toll. but then an astonishing revelation. two italian independent experts, assigned by the court to review that dna evidence -- >> [ speaking foreign language ]. >> reporter: -- blasted the findings of the prosecution's star forensic expert. >> these independent experts came forward saying there is no evidence on the knife and this little bra clasp also had no dna of the young man. >> it's a great moment when what you've said through careful, long analysis is repeated by independent people that the judge appointed in this case. >> reporter: and it didn't end there. next came a blistering critique of how the evidence was collected. the independent experts explained the proper p pcedures required by international standards. evidence must be placed into paper, not plastic bags to avoid moisture. >> you're supposed to photograph it, get a pair of tweezers that's never been used fresh from the box.

you pick up that piece with gloved hands, and you put it into a paper bag. >> reporter: it turns out there are three things that can destroy dna's value -- moisture, heat, and law enforcement. take a look at this. the forensic police's own crime scene video. it shows evidence, notably that all-important bra clasp, being picked up from the floor, passed around, and then placed back on the floor. >> in this remarkable moment, you know, this evidence is going to be key in this case, they take that bra clasp and lay it on the floor. >> reporter: and those gloves, so important for preventing contamination? the court saw a close-up photo of one investigator's hand. check out that dirt. the experts said the bra clasp should never have been admitted as evidence at all. and the display of sloppiness prompted courtroom observers to laugh and shake their heads in amazement. it's humiliation for the prosecutors and a home run for knox's lead italian lawyer.

>> you must be optimistic after today. >> we always optimistic because we know amanda has always told us the truth. >> reporter: tensions ran high. the judge even shouting to silence the lead prosecutor. >> [ speaking foreign language ]. >> pounding on the desk. >> reporter: be quiet. >> yeah, be quiet. >> reporter: the hearing resumes tomorrow when prosecutors are set to cross-examine the independent experts. but these startling discoveries have fueled speculation that this case has been a huge miscarriage of justice. >> taking away the material evidence destroys the case. and i don't think that they can go very much farther with it. >> reporter: so do you think this is the beginning of the end? >> i'm still not going there. i don't make those predictions. can't do it. >> i think we're moving definitely in the right direction. >> reporter: you were in tears when court ended today. why was that such an emotional moment? >> you know, seeing amanda, seeing all of us get emotional, and to be able to hug her and

just tell her, do you u e the light now? can you see it now? >> reporter: happy crying for the first time? >> happy crying, yeah. >> reporter: i'm elizabeth vargas for "nightline" in new york. >> glimmers of hope for a family. our thanks to elizabeth. up next, from bong hits on screen to policy meetings in the white hohoe. the star of "harold and kumar" hahanever given an interview since joining the obama administration until tonight. 66% of new products have some kind of intelligence built in... refrigerators order groceries from the store. washing machines run when energy prices are lowest... and dryers call for service before they break down. air conditioners respond to local weather reports. software gives businesses new ways to connect to customers. by making things smarter, life gets better. that's what i'm working on. i'm an ibmer. i'm an ibmer. i'm an ibmer. let's build a smarter planet.

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some actors adopt foreign babies, some launch perfume or salad dressing lines, but kal

penn, one half of the comedy stoner duo "harold and kumar," had different dreams. two years ago he walked off the set of the fox hit "house" and into an office at the white house. and today he's walking out with the first exclusive answers to how and why. here's abc's jake tapper. >> i'm kalpen modi from the white house office of public engagement. >> reporter: today was the last day of work for kalpen modi at the white house. you probably know him better as kal penn, his stage name, or even more -- >> no eating until we get to white castle. >> reporter: as kumar, from the "harold and kumar" film franchise. >> i'm not joining the mile-high club with you. >> what about the really high club? >> reporter: or as the suicidal dr. kutner from "house." >> she's faking it. it's a cry for attention. >> get out of my house. >> reporter: or a terrorist from "24." lots of actors campaign for democratic politicians and presidential candidates. but penn may be the only one in recent memory to go on hiatus from acting to work for a politician. >> you know i've been trying to

interview you for like 2 1/2 years. >> i understand. i appreciate that. >> reporter: but you haven't let me do it until your departure. >> correct. >> reporter: because? >> our jobs are really, you know, kind of keep your head down and do good work. it just wasn't -- it wasn't the old life. >> reporter: since 2009, penn has worked under obama senior adviser valerie jarrett as associate director of public engagement, focusing on young americans. slaving away in this small office with five co-workers. working with president obama, talking to students here and across the country. >> our offffe doesn't handle policy but we help kind of bridge the gaps between policy so we -- >> reporter: you explain what's going on in policy to the public? >> exactly. and then vice versa. so if there's a group of young folks that are particularly concerned about an issue and they want to bring in, you know, 10 or 12 folks, we'll put them in a room with some of our policy team and kind of link up that way. >> reporter: one of his jobs, engaging those elusive young

voters who turned out in droves for obama in 2008. he acknowledges that the young idealistic throngs have changed in attitude a bit, though he insists they're not less inspired. >> i think what i've seen is that there is a realization that change is not a light switch, that if it was easy to just flip on a light switch and change everything then somebody would have done it before and it's actually a very laborious process, that it's very slow. so i wouldn't say it's disillusionment. i would say it's understanding the process. >> reporter: a lot of hollywood actors, and i don't mean that in a derogatory way, but a lototf hollywood actors appear at rallies. you're the only one i ever heard of who has then taken a job, and a behind-the-scenes job really, with the administration. what could possibly motivate you to do that? >> i have friends and folks who i knew who were over in iraq and afghanistan. i had buddies who had huge student debt, people that got kicked off their health insurance plans for one reason or another. so that was my kind of decision

to get involved on a personal level. >> reporter: i know that this is your whole thing, that you're not any different than anybody else who works here. >> but it's true, jake. i don't mean to sound boring. it's just the reality ofofur day-to-day -- >> reporter: i know. but it is a little different. you put your career in hollywood a very high-profile one, and you've worked in some movies that have made a lot of money. >> if you talk to the numbers of staffers here that have families and multiple kids at home and you talk about folks who have been working jobs that they worked their lives for and then took a break for two years and are not making as much money as they had before and putting their family life on hold, i mean, those are the real stories. >> reporter: i guess we should cancel the segment right now. >> i would say do the segment on everybody else. you know. but i r rlly do think that. that's what kind of keeps me going. that's what i see on a daily basis. and it's sort of like the awe-inspiring basis of this

place. >> reporter: one of penn's fondest moments was a late night in january when he accepted a painting to be given as a gift to chinese president hu jintao. >> you're standing there. you have to -- the south portico of the white house at midnight. it's freezing cold outside. and you're receiving the painting. >> it's no big deal. >> on behalf of the president that he's going to give to another world leader, which i i kind of -- you know, you tak a moment and kind of realize where you are. and it's pretty humbling. >> reporter: he's clearly loved every minute here. so this is where all the magic happens? >> correct. >> reporter: you're in this office with six other people. five other people. >> correct. >> reporter: it's kind of hot in here. >> it is. there's a little temperature control over there, but, you know -- >> reporter: it's not glamorous is what i'm saying. >> no. >> reporter: worker bees. >> yes. they're -- it's a great team of people here. i think they're putting in some hours doing some good work. >> reporter: penn says the plan was always to work for two years and go back to hollywood, where work awaits. a guest role on "how i met your mother."

>> she means you. >> reporter: "harold and kumar 3." and some offers far more lucrative than the $41,000 a year job he left behind today. though you get the impression he will miss it quite a bit. this is jake tapper for "nightline" at the white house. bit. this is jake tappepefor "nightline" at the white house. bring it. getting it clean again is easy with bounty. in this lab demo, one sheet of bounty leaves this surface as clean as 2 sheets of the bargain brand. ♪ why use more when you can use less? ♪ super durable. super absorbent. super clean. bounty. the one-sheet clean picker-upper. [ man ] i love you guys. [ laughs ] i mean, just, you know, the whole heist thng/ just putting jewels in teddy bears. this guy's wearing a wire the whole time. right? look at that! he's wearing a wire!/ [ laughs ] all right, let's do this. all right? before my wife changes her mind. go.

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well, as we told you at the top of the show, despite all the sound and the fury on capitol hill this week, it appears we are no closer to avoiding a predicted economic disaster over the debt limit. let's bring in abc's senior political correspondent jon carl. please tell us, jon, there is some whiff of bipartisan compromise in the air. >> reporter: well, i would love to tell you that. there is no whiff quite yet. i can tell you in fact they are moving in the exact opposite

direction. the house of course passed that republican version of the debt ceiling bill, john boehner's bill. the senate acted immediately to reject it. and now i am told that the house is going to move forward tomorrow at 1:00 with a vote on the democratic version that harry reid has put forward and they're going to reject that. so we will have republicans rejecting the democratic deal, democrats rejecting the republican deal. house, senate, no action. but clearly there are negotiations going on behind the scenes. >> let's talk about worst case scenario. if the markets open on monday and tank, is there some trigger mechanism to avoid a cataclysmic event? >> reporter: well, you know, there are certainly emergency powers the president can exercise. but before we get there, bill, what i expect to see happen is that the two sides will negotiate late into the night tomorrow. if they can get a deal tomorrow, by saturday night by about midnight, they can still pass something in time in both the house and the senate. >> jon and his team will be

feeding abcnews.com with the latest blow by blow all weekend. much obliged, jon, thanks. and with so much rhetoric flying these days, we thought it might be helpful to end aumultuous week with a little perspective. so here we go. the debt crisis by the numbers. >> $14.3 trillion. the size of our national debt. or roughly $46,000 for every man, woman, and innocent child. 2.4 trillion of that is the amount added to the debt under barack obama. 6.1 trillion the amount added under george w. bush. $74 billion, the amount of casas the u.s. treasury has on hand. 76 billion, the amount of cash apple computer has on hand. 78. the number of times the debt ceiling has been raised since 1960. times under democratic presidents. 49 times under republicans. 330, the number of times a republican senator voted to raise the limit in the decade

before barack obama was elected. 3, the number of times since. and 3 is also the number of times then senator obama either voted against raising the debt limit or didn't vote at all. 18, holes of golf played by the president and speaker in an effort to reach a grand bargain. 9, number of urgent white house meetings in an effort to reach a grand bargain. 0, the number of grand bargains. 62, percentage of americans who told abc news that we need to cut spending and raise taxes to fix our problem. 34, percentage of strong tea party members whwhagree with that kind of compromise. 1, number of times john mccain accused hard line tea party representatives of living in a "lord of the rings" fantasy world. >> then democrats would have no choice but to pass a balanced budget amendment and reform entitlements and the tea party hobbits can return to middle earth, having defeated mordor.

>> reporter: 50, president obama's age on his birthday this thursday. 2, number of chicago fundraising parties he's planning to attend on wednesday under the assumption a deal will get done. >> we're confident this will be resolved. obviously, if it's not we'll address the schedule accordingly. >> reporter: $1.2 trillion. the amount of dollars owned by china, whose state-run news agency wrote a scolding editorial today about the ugly impact on the donkey and the elephant fight. 70 million, the approximate number of checks the government cuts each month to everyone from soldiers to retirees to astronauts. and the number of checks that won't go out in august if the ceiling isn't raised? well, we'll just have to put a big question mark there because that has never happened. the national plot thickens. thank you for watching abc news. we hope you'll check in on "good morning america."