. >> abc's devin dwyer has more. >> reporter: for the first time, a look at what the victims saw inside navy yard building 197. chilling new fbi video shows a killer on the prowl. aaron alexis, armed with a sawed-off shotgun, going room-to-room. >> there are indicators that alexis was prepared to die during the attack. and he accepted death as the inevitable consequence after his actions. >> reporter: alexis roamed freely for an hour and a half. entering a navy yard parking garage just before 8:00 a.m. moments later, cameras catch him walking in through the first door, without any security check. he then went to the fourth floor, took out his gun and began stalking targets. >> it appears that mr. alexis, in a scenario that we've seen far too often, quite frankly, was a mentally unstable individual. >> reporter: clues to his mental illness were found on the murder weapon. these fbi photos show etchings on the gun's side. one reads, end to the torment. another, better off this way. and in his computer file, the fbi found this note. >> all low-frequency attack, is what i've been subject to

. >> devin dwyer joins us from washington with the very latest. good morning, devin. >> reporter: that's right. the federal government will shout down in roughly 90 hours. that's plenty of time to reach a deal. but right now, no one's at the negotiating table. the battle over obama care is pushing us over the brink. >> defund this bill that's forcing people into part-time work. >> you can huff. you can puff. for 21 hours. but you cannot blow the affordable care act away. >> reporter: that's exactly what republicans are determined to do. a dispute that could force a government shutdown? just four days. president obama says his health care law is nonnegotiable. >> the affordable care act is here to stay. >> reporter: today, the senate is expected to vote to keep the government open and keep money flowing to obama care. but that plan doesn't sit well with house speaker john boehner. >> the american people don't want the president's health care bill. and they don't want the government to shut down. now, the president says i'm not going to negotiate. we

d devin dwyer has been working all the angles. he has the latest. good morning, devin. >> reporter: we haven't seen a federal government shutdown since 1996. it could happen at the stroke of midnight. that is when the government runs out of money just as obama care is set to kick in. the clocking ticking towards a shutdown. the halls of congress are eerily quiet. no negotiations. no emergency meetings. the bitter dispute over obama care is spilling out on the air waves. >> the president is the one saying i will shut down government if you don't give me everything i want on obama care. >> it's wrong to use a shutdown of government as a lever to make change. >> reporter: to keep the government open, house republicans want to delay the health care law by one year and repeal a tax on some medical devices. senate democrats and president obama are refusing to budge. >> your hate for this president is coming before the love of this country because if you loved this country, you would not be closing it down! >> we're fighting for the american people. >> repo

. >> devin dwyer joins us from washington with the very latest. the federal government will shout down in roughly 90 hours. that's plenty of time to reach a deal. but right now, no one's at the negotiating table. the battle over obama care is pushing us over the brink. >> defund this bill that's forcing people into part-time work. >> you can huff. you can puff. for 21 hours. but you cannot blow the affordable care act away. >> reporter: that's exactly what republicans are determined to do. a dispute that could force a government shutdown? just four days. president obama says his health care law is nonnegotiable. >> the affordable care act is here to stay. >> reporter: today, the senate is expected to vote to keep the government open and keep money flowing to obama care. but that plan doesn't sit well with house speaker john boehner. >> the american people don't want the president's health care bill. and they don't want the government to shut down. now, the president says i'm not going to negotiate. well, it sorry. but it just doesn't work that way.

devin dwyer, abc news, washington. >>> the state department has renewed its global terror alert after americans to be careful about the threats worldwide. and that potential targets include large public gathering places, including during the holidays. >>> we're looking at the sophistication of the terror plot in nairobi. the investigators say the terrorists rented a store in that mall for three months. it was used for a base to plan the attacks and stash weapons. there's reports that some of the attackers slipped out during the siege. forensics teams are looking for clues. >>> at the united nations, historic talks begin between the u.s. and iran. john kerry, sitting down with the iranian foreign minister on iran's nuclear weapons. it marks one of the highest level contacts between those two countries in years. >>> lawmakers have taken one step back from the brink of a government shutdown. a unanimous vote would allow to come to the floor for a possible passage. the vote came after ted cruz finished his nearly 22-hour talk-a-thon against the president's health care plan. cruz was asked