Updated 4/19/13 5:15 am
One suspect in this week's deadly Boston Marathon bombing was killed after a police shootout, and a second suspect, identified by officials as Dzhokhar Tsarnaev, remains at large and the subject of a manhunt, police said early this morning.
Tsarnaev, the man the FBI identified Thursday only as Suspect 2 in photos related to the marathon bombing investigation, is on the loose and is armed and dangerous, police said. The 19-year-old is the target of a "massive manhunt," Massachusetts Gov. Deval Patrick said today.
"We believe this is a terrorist, we believe this is a man that's come here to kill people," Boston Police Commissioner Ed Davis said early this morning.
The first suspect was killed after exchanging gunfire with police officers, during which multiple explosive devices were detonated, police said. Officials at Beth Israel Hospital reported they received one patient who later died, but would not confirm it was the first suspect.
That patient came in under guard and had suffered blast, shrapnel and so many gunshot wounds that caregivers were "unable to count" them.
The suspects had been in the United States for at least two years and, because of the skill with which they engaged police, likely had paramilitary training, federal law enforcement sources told ABC News. A neighbor of Tsarnaev's said he had been in the country at least since he was seven years old.
One police officer was also injured in the firefight and is in critical condition at a hospital. Authorities said the suspects were also responsible for the death of an MIT police officer Thursday night.
Police in Watertown, Mass., a suburb of Boston, blocked off at least one town street and multiple police cars, ambulances and fire trucks surrounded the scene after the firefight in a residential neighborhood. Boston officials said on Twitter that all public transportation has been suspended amid the manhunt.
Massachusetts state police have tweeted guidance for Watertown residents to stay in their residences and not answer their doors unless it is for an identified police officer. Police are "going door by door, street by street, in and around Watertown. Police will be clearly identified. It is a fluid situation," according to the state police tweet.
Police said the violent ordeal began around 10:30 p.m. Thursday evening when a 7-Eleven convenience store was robbed in Cambridge, Mass., shortly before the MIT officer was shot. The suspects then hijacked a Mercedes and drove to Watertown while being pursued by police. The chase ended in a firefight that left one suspect dead, while the other managed to slip away, police said. Federal law enforcement sources told ABC News the suspects admitted their role in the Boston Marathon bombing to the carjack victim.
The Monday bombing near the finish line of the Boston Marathon killed three people and injured more than 170 more. The FBI released images Thursday evening of the two suspects in the case.
ABC News' Aaron Katersky contributed to this report.
(BOSTON) -- Authorities have a clear picture of a potential suspect in the Boston Marathon bombings and are in the process of identifying that individual, sources told ABC News on Wednesday.
ABC News' Boston affiliate WCVB reported surveillance video taken from cameras at Lord & Taylor along the marathon route were key to spotting the individual in question.
Other news organizations recently reported a suspect already had been taken into custody, but both the Boston Police Department and the FBI said no one has been arrested in connection with the bombing.
In the midst of the conflicting reporting, a federal courthouse in Boston was evacuated because of a bomb threat, a source with the U.S. Marshals told ABC News. As of this report, no suspicious devices have been found there.
A pair of blasts erupted Monday afternoon near the finish line of the Boston Marathon, killing three people and injuring more than 170 others.
Authorities said they have been analyzing thousands of photos of the event and tracking down as many leads since the bombing. On Tuesday ABC News reported part of a pressure cooker bomb had been recovered from the scene with wires, shrapnel and a circuit board. A Fagor brand pressure cooker like the one used in the attack can be bought from major retail outlets for around $140. Investigators said there was not enough evidence to determine if the second bomb was also made from a pressure cooker.
The evidence has been sent to the FBI's lab in Quantico, Va., where law enforcement sources said the parts could provide a break in the case.
Investigators will use every clue, from the pressure cooker's manufacturer and retailers to the types of nails used in the shrapnel, to try and find out from where the bomb parts were purchased and by whom, the sources said.
Richard Clarke, former White House counter-terrorism advisor and now ABC News consultant, said that while pressure cooker IEDs have been found in Afghanistan and Pakistan, that doesn't necessarily point to foreign involvement, as the pots are so widely available and instructions for how to build the bombs are easily accessed online by anyone.
"It doesn't tell you much about who did it... But it does give you a lead perhaps of where it came from," Clarke said. "They [investigators] may be able to trace back a pressure cooker."
Along with tracking down the origin of the bomb parts, authorities are painstakingly going through hundreds of pictures and videos from the site of the bombing, hoping, as Clarke put it, to "stitch" together a picture of what exactly happened. It was possibly during this process that authorities identified the potential suspect spotted Wednesday.
Despite more than 48 hours passing without a suspect named, Clarke said he's confident the authorities will get their man.
"It may take a while, but this will be solved," he said.
Copyright 2013 ABC News Radio