A trail of blood led to accused Boston Marathon bomber Dzhokhar Tsarnaev as he hid inside a boat after eluding one of the biggest manhunts ever staged in the United States.
Exhausted and wounded, the 19-year-old, whose brother was killed earlier Friday, staged a final gun battle with his pursuers before he gave in to Federal Bureau of Investigation (FBI) negotiators.
Tsarnaev was in "serious condition" at Beth Israel Deaconess hospital in Boston as the city celebrated his capture with street parties.
Those festivities could so easily have been a new night of anguish for the Boston region, facing growing tension after the bombs left at the marathon finish line on Monday killed three people and injured about 180.
Boston investigators had just held a press conference at which they virtually admitted that Tsarnaev had escaped when the lucky break came.
Tsarnaev had already been wounded overnight in a gun battle with police in which his elder brother Tamerlan was killed.
"We know he didn't go straight to the boat," which was outside a security zone that had been painstakingly searched by thousands of heavily-armed officers, said Boston police chief Ed Davis.
"We found blood in the car that he abandoned, we found blood inside the house behind the perimeter," he added. "We had no indication that he had gotten outside of the perimeter. It was very chaotic."
"A man had gone out of his house after being inside the house all day" because of a lockdown ordered by authorities, Davis explained to reporters after the dramatic capture.
"He saw blood on a boat in the backyard. He then opened the tarp on the top of the boat and he looked in and saw a man covered with blood."
The man telephoned police and at the same time, a police helicopter used infra-red equipment to determine there was a human in the boat.
"We exchanged gunfire with the suspect who was inside the boat, and ultimately, the hostage rescue team of the FBI made an entry into the boat and removed the suspect who was still alive," Davis told a press conference.
The negotiation team had tried to make Tsarnaev give himself up.
Police teams also fired flash grenades in a bid to stun the suspect into surrender.
Tsarnaev was given first aid on the lawn next to the boat before being taken away in an ambulance.
The boat had not been searched before because it was outside of the police perimeter set up as the hunt intensified.
Noisy celebrations erupted on Franklin Street, where the standoff unfolded, and beyond after the arrest.
Crowds cheered and applauded police as they packed up equipment and drove away from the house. There were also festivities around Boylston Street in central Boston -- scene of Monday's carnage.
"Let's Go Boston" and "USA, USA," crowds chanted, with some people climbing onto car roofs while others danced in the streets.
"It has been so tense all week," said neighbor Susan Nolan. "I was so nervous when I heard that the police were planning to pull out and he had not been caught."