WATERTOWN, Mass. April 19, 2013— -- The alleged Boston Marathon bomber who hid from authorities for more than 20 hours was captured tonight by police, sending cheers up through the Watertown neighborhood where he was found.
Dzhokhar Tsarnaev, 19, was discovered by a homeowner lying in a boat in the man's backyard around 7 p.m. The man noticed blood on the boat, spotted a body inside the boat and called 911, according to Boston Police Commissioner Ed Davis.
According to police, a helicopter with infrared technology then located Tsarnaev in the boat and noted that he was moving about within it. The helicopter directed officers on the ground to the boat, where they briefly exchanged gunfire shortly before 7 p.m.
Police halted their gunfire and sent hostage negotiators to try and talk Tsarnaev out of the boat Davis said.
But the suspect was not responsive, and after about an hour and 45 minutes, officers went to the boat and took Tsarnaev into custody.
His arrest sparked a spontaneous celebration in Watertown with people high fiving police, chanting Boston strong and USA.
"We got him," Boston Mayor Tom Menino tweeted immediately after Tsarnaev was arrested. "I have never loved this city & its people more than I do today. Nothing can defeat the heart of this city .. nothing."
The Boston police department also sent out a tweet in the aftermath trumpeting, "CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody."
Tsarnaev and his brother, Tamerlan Tsarnaev, 26, are believed to be behind the bombing of the Boston Marathon on Monday that killed three individuals and injured more than 170.
Tsarnaev was then transported away from the scene in an ambulance, as law enforcement officials and onlookers clapped and cheered.
The alleged bomber had been shot by police during gunfire nearly 24 hours earlier, when he and his brother allegedly shot and killed an MIT police officer and then engaged in a shootout with cops.
Police said tonight that there were some 200 rounds of ammunition, as well as improvised explosive devices and homemade hand grenades found at the scene of the shooting. Tamerlan was killed in the gunfire, but Dzhokhar fled on foot into Watertown.
Police locked down a 20-block section of Watertown today and searched door-to-door with heavily armed SWAT team members.
But police said at a press conference after the standoff ended that Tsarnaev had escaped their manhunt and hid himself in the boat just one block outside of the perimeter they were searching.
"We know he didn't go straight to the boat," said Watertown police chief Edward P. Deveau. "We found blood in the car he abandoned and we found blood in a house inside the perimeter. We had no information that he had gotten outside the perimeter, but it was very chaotic this morning. We had a police officer who was shot and bleeding."
"We had a perimeter that we thought was solid and we did that but we were about one block away," Deveau said.
Tsarnaev is in "serious" condition at a hospital tonight, Davis said.
A senior Justice Department official told ABC News that federal law enforcement officials are invoking the public safety exception to the Miranda rights, so that Tsarnaev will be questioned immediately without having Miranda rights issued to him.
The federal government's high value detainee interrogation group will be responsible for questioning him.
The Miranda exemption exists to protect the public safety from another attack, according to the official.
The capture was quickly followed by a press conference with a host of law enforcement officials, ranging from the Boston police commissioner to the FBI and the U.S. Attorney who will ultimately prosecute the case, all of whom praised the work of officers and the public.
President Obama condemned the actions of the bombers today, though he warned the public not to jump to conclusions about motivations.
"In this day of instant reporting, tweets, and blogs, there is a temptation to latch onto any bit of information, sometimes to jump to conclusions, but when a tragedy like this happens, with the public safety at risk and the stakes so high, it important to do this right," Obama said. "That's why have an investigation, that's why we relentlessly gather the facts, that's why we have courts."
"Whatever hateful agenda drove these men cannot, will not prevail," he said, "and whatever they thought they could achieve failed because the people of Boston refuse to be intimidated, and we as Americans refuse to be terrorized."
The rush of developments this evening came after a day of searching turned up nearly no signs of Tsarnaev, and government officials finally lifted a city-wide lockdown order that had been in effect since the morning.
At a news conference around 6 p.m., Gov. Deval Patrick lifted the lockdown order, saying they had not found the suspect in Watertown.
Shortly after the Patrick's announcement, Watertown homeowner David Henneberry walked into his backyard and saw something amiss with his boat, according to Henneberry's neighbor, George Pizzuto.
"He looked and noticed something was off about his boat, so he got his ladder, and he put his ladder up on the side of the boat and climbed up, and then he saw blood on it, and he thought he saw what was a body laying in the boat," Pizzuto said. "So he got out of the boat fast and called police."
Henneberry notified police, and minutes later gunfire erupted and dozens of law enforcement officers rushed to secure a perimeter around Franklin Street in Watertown, where residents were immediately warned to stay indoors and "shelter in place."
"That boat's his baby. He takes care of it like you wouldn't believe. And they told him it's all shot up," Pizzuto said. "He's going to be heartbroken."
Earlier in the day, police in took three individuals into custody in connection with the search for Tsarnaev.
Lt. Robert Richard of New Bedford, Mass., said three "college age" individuals were taken in for questioning by the FBI. New Bedford is less than 15 miles north of Dartmouth, Mass., where Tsarnaev attends college.
The hunt for the brothers heated up Thursday night after they were reported to have robbed a convenience store, although police said today that the report was false. Police have recovered surveillance video of the Tsarnaevs buying gas in Cambridge.
They are believed, however, to have ambushed and killed MIT security officer Sean Collier as he sat in his patrol car Thursday night.
They later hijacked a Mercedes SUV Thursday night and told the driver that they were the Marathon bombers, police said. The vehicle was spotted by police about 12:50 a.m. today, sparking a chase and gunbattle that included the brothers tossing explosives at the pursuing cops, police said.
Tamerlan Tsarnaev was killed in the gun fight and Dzhokhar Tsarnaev was able to get away, fleeing on foot in Watertown, police said.
Beth Israel Hospital said a patient, apparently Tamerlan Tsarnaev, came in under guard and had suffered blast and shrapnel injuries as well as so many gunshot wounds that caregivers were "unable to count" them.
Police officer Richard Donohue Jr., 33, was injured in the firefight and is in critical condition at a hospital.
ABC News' Aaron Katersky contributed to this report.