After two bombings killed three and injured over 176 on April 15, police chased two suspects across Cambridge and Watertown starting around 10:30 p.m. Thursday night. After one suspect was shot during a shoot-out in Watertown in the early morning hours on Friday, police worked together with FBI, National Guard, and other units to find the second suspect. The search concentrated on Watertown, and investigators eventually closed in on the suspect in a Watertown backyard.

UPDATED: April 20, 2013, at 3:50 a.m.

A massive manhunt that began with the shooting of an MIT police officer in Cambridge Thursday night and paralyzed the greater Boston community for a full day concluded Friday evening with the apprehension of the second marathon bombing suspect in a standoff in Watertown.

Dzhokhar A. Tsarnaev, a 19-year-old Cambridge resident, was taken into custody Friday night after police found him hiding inside a dry-docked boat in the backyard of a Watertown house. Covered in blood and possibly wounded from two standoffs with law enforcement, Tsarnaev was taken to Beth Israel Deaconess Medical Center in “serious condition,” Boston Police Commissioner Edward F. Davis said.

Tsarnaev’s 26-year-old brother, Tamerlan Tsarnaev, was fatally shot in a firefight with police in Watertown early Friday morning. Along with his brother, he is suspected to have been a perpetrator of Monday’s bombings at the Boston Marathon, which killed three and injured more than 170. Dzhokhar Tsarnaev was a part of the Friday morning skirmish as well but evaded capture by the combined forces of municipal, state, and federal law enforcement for much of the day Friday.

With Tsarnaev at large until the FBI finally captured him at 8:45 p.m. Friday, Massachusetts Governor Deval L. Patrick ’78 ordered much of the greater Boston area to stay indoors and close businesses for the day. With the MBTA closed at the governor’s request and police forces forbidding all traffic into or out of Watertown, the combined police forces launched a door-to-door search of a 20-block section of Watertown, where the younger Tsarnaev was believed to be hiding. The Massachusetts State Police Bomb Squad was also deployed early Friday to search the area for any explosive devices, the Cambridge Police Department wrote in a statement early Friday.

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A Round of Applause

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Map of Manhunt for Boston Marathon Bombing Suspect

After a day of futile searching, the governor lifted the city-wide lockdown shortly after 6 p.m., and for the first time all day, Watertown residents trickled outside of their homes and offices and into the streets.

Less than an hour after the ban was lifted and the chances of a quick capture seemed to have passed, a Watertown resident walked into his backyard and noticed blood on the cover of his boat, which was dry-docked there. Upon lifting the tarp from the top of the boat, the resident saw a man coated in blood sitting inside the boat, said Davis.

The Watertown resident returned inside and called law enforcement authorities, who rapidly mobilized and arrived at his house. According to Davis, the scene was located outside the perimeter of the door-to-door searches conducted earlier in the day.

Heavily armed forces, along with a heat-sensing State Police helicopter hovering overhead, surrounded the boat. The approach was cautious due to the risk that Tsarnaev, who was still shrouded by the boat’s tarp, had strapped deadly explosives to his body. After nearly an hour of gunfire and “flash bang” stun grenades used to disorient Tsarnaev, an FBI hostage rescue team closed in on the teenage suspect.

U.S. Attorney Carmen M. Ortiz said Tsarnaev was not read the customary Miranda Rights, which inform suspects of their civil liberties with respect to questioning and are normally required reading before interrogation. But when a suspect is deemed to pose an immediate threat to law enforcement officers or the general public, police can invoke the “public safety” exception—the only exception to the Miranda rule—and engage in interrogation of the suspect without reading the Miranda Rights.

News of Tsarnaev’s capture spread quickly over television and Twitter, offering Bostonians who had spent much of the week in fear a chance to breathe a sigh of relief and celebrate law enforcement’s victory over the alleged terrorists. In Watertown, just blocks from the final shootout, residents lined the streets and chanted, “USA! USA!” as emergency vehicles and state troopers exited the area. Residents from across the greater Boston area gathered on the Boston Common late Friday night, where just days before they had come together to mourn the victims of the marathon bombings.

At a press conference at 9:30 p.m. Friday, nearly 24 hours after the manhunt began, law enforcement officials from the FBI, the cities of Boston and Watertown, and the Massachusetts State Police stood beside politicians and public servants to celebrate the successful capture of the younger Tsarnaev.

“We are eternally grateful for the outcome here tonight. We have a suspect in custody,” Alben said. “We’re so grateful to bring justice and closure to this case.”

But officials stressed that the capture is just the beginning of the broader investigation into how and why the suspects were driven to terrorism. Ortiz said that her office will begin the difficult process of reconstructing the case and eventually prosecuting the surviving suspect.

Addressing the nation Friday night, President Barack Obama cautioned against jumping to conclusions or judgments about the case before all the details are worked out. Still, he said, Friday night’s capture and arrest marked the end of a sad chapter for Boston.

“Whatever hateful agenda drove these young men to such heinous acts will not prevail,” Obama said. “Whatever they thought they could ultimately achieve, ultimately failed.”

Though the pursuit of the bombers began almost immediately after Monday’s bombings, it was not until the seemingly random murder of an MIT police officer Thursday night that law enforcement officials advanced the case, suid Massachusetts State Police Colonel Timothy P. Alben in an impromptu press conference convened shortly before 4:30 a.m. Friday and again at Friday night’s conference after Tsarnaev’s capture.

In a statement released early Friday morning, the Cambridge Police Department wrote that they first received a report around 10:20 p.m. Thursday that shots had been fired on the MIT campus. When they arrived on the scene at 10:30 p.m., CPD found an MIT officer, in his car, with multiple gunshot wounds. That officer, identified as 26-year-old Sean Collier, was transported to Massachusetts General Hospital, where he was declared dead on arrival, according to the Middlesex County District Attorney’s Office.

Cambridge police also received reports of an armed robbery at a 7-Eleven in Central Square at 10:30 p.m. Though that incident was initially thought to be related to the murder, Alben said Friday that law enforcement had determined the two were unrelated, but that the bombing suspects were in the store at roughly the time of the robbery.

Shortly thereafter, they said, an armed hijacking occurred around Third Street in Cambridge, when two male suspects held the owner of the car, a Mercedes SUV, at gunpoint. The car owner was released roughly half an hour later at a gas station off Memorial Drive.

When the stolen Mercedes was spotted in Watertown by police in that area, Alben said, a mass chase ensued as CPD, Massachusetts State Police, and the FBI joined the effort. It ultimately resulted in a firefight between law enforcement and the two suspects, who threw improvised explosive devices and homemade grenades and traded some 200 rounds of gun shots with law enforcement, Davis said.

“This is the stuff that in an urban police department, it’s almost unheard of,” Davis said Friday night after Tsarnaev’s capture.

In his haste to escape police, Tsarnaev drove over his older brother’s body, which was bound with explosives, law enforcement officials said.

In addition to Tamerlan Tsarnaev, and the MIT police officer, one MBTA Transit Police officer was shot in the gunfire exchange en route to Watertown Thursday night. That officer is in stable condition, MBTA officials said Friday.

Alben identified Dzhokhar Tsarnaev as the same man suspected of helping to carry out Monday’s bombing and seen wearing a white hat in surveillance video from the marathon. Officials believe Tamerlan Tsarnaev is the same man seen wearing a black hat and sunglasses in other surveillance video.

The Tsarnaev brothers immigrated to the United States a decade ago from Chechnya and lived in central Cambridge. Dzhokhar Tsarnaev attended Cambridge Rindge and Latin School and worked part-time as a lifeguard at Harvard’s Malkin Athletic Center, former classmates said Friday.

In response to the ongoing search for the alleged terrorist, the University closed all operations on Friday, advising students to stay inside as much as possible.

—Matthew Q. Clarida and Samuel Y. Weinstock contributed to the reporting of this story.

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu. Follow him on Twitter @npfandos.

—Staff writer Nikita Kansra can be reached at nikitakansra@college.harvard.edu. Follow her on Twitter @NikitaKansra.

This article has been revised to reflect the following correction:

CORRECTION: April 22, 2013

An earlier version of this article misquoted Boston Police Commissioner Edward F. Davis as describing the capture of the marathon bombing suspect as something “that an urban police department has never heard of.” In fact, Davis described the manhunt as something “that in an urban police department, it’s almost unheard of.”