After a manhunt that lasted nearly 24 hours, a trail of blood in a suburban backyard led police to the remaining suspect in the Boston Marathon bombings: 19-year-old Dzhokhar Tsarnaev.

He was arrested Friday night after a resident of Watertown, just outside of Boston, found him holed up in a boat in his backyard, covered in blood.

The resident called police. Officers quickly surrounded the area as police helicopters hovered above. They exchanged gunfire with the suspect, then tried setting off flash-bang grenades to coax him out of the tarp-covered boat.

Tsarnaev was eventually apprehended around 8:45 ET. He was taken to hospital in serious condition, police said.

His brother and the other suspect in Monday’s twin bombings, 26-year-old Tamerlan Tsarnaev, was killed in a shootout with police the night before.

As police officers emerged from the cordoned-off area after Tsarnaev’s arrest, bystanders erupted in cheers and applause .

"CAPTURED!!! The hunt is over. The search is done. The terror is over. And justice has won. Suspect in custody," Boston police tweeted.

“We are so grateful to bring justice and closure to this case,” Massachusetts State Police Col. Timothy Alben told reporters. “We’re exhausted, folks, but we have a victory here tonight.”

The dramatic capture capped off an intense chase throughout the Boston area, which began late Thursday night with what police called the “vicious assassination” of a campus officer at the Massachusetts Institute of Technology in Cambridge.

Sean A. Collier, 26, was gunned down just before 11 p.m. Thursday. Shortly after, police allege, the Tsarnaev brothers carjacked a vehicle, prompting a police pursuit that ended with a shootout in Watertown.

Police said Friday that roughly 200 rounds of gunfire were exchanged in the incident and the suspects threw explosive devices at officers.

The older Tsarnaev brother was gravely injured and later pronounced dead in hospital. Dzhokhar Tsarnaev escaped, police allege, reportedly running over his brother with a car to get away. Police were forced to virtually shut down Boston and the surrounding area, halting vehicle traffic and ordering people to stay inside their homes.

Throughout Friday, armed SWAT and FBI officers and snipers took up positions on various buildings around the neighbourhoods. Helicopters hovered in the sky and armed troop carriers patrolled the streets as authorities searched for the suspect.

Boston paralyzed

Businesses were asked to remain closed for the day and Friday evening’s Boston Bruins and Boston Red Sox games were postponed.

Eerie photos circulating online show empty roads and highways in the normally bustling Boston area, with no pedestrians in sight.

Around 6 p.m. ET, police said they had canvassed a large swath of Watertown and nearby neighbourhoods, but found no trace of Tsarnaev. They told residents that even though the manhunt was still on, it was finally safe to go outside.

That’s when the resident who had a boat in his backyard emerged from his house and noticed blood on the ground. He followed the crimson stains to the boat, lifted the tarp and made the startling discovery.

It was not immediately clear what kind of injuries Tsarnaev sustained during the manhunt.

Boston Police Commissioner Ed Davis said he didn’t know if the college student was struck during Friday night’s shootout. Tsarnaev could have been injured in Thursday’s standoff, Davis said.

Tsarnaev and his older brother, who emigrated to the U.S. from a region near Chechnya roughly a decade ago, are accused of setting off two bombs near the finish line of the Boston Marathon on Monday, killing three and injuring more than 180.

The explosives were contained in pressure cookers packed with ball bearings and nails to inflict as much damage as possible, authorities said.

The FBI first released surveillance images of the two suspects late Thursday afternoon, asking the public to help identify them.

The young men were seen along the marathon route, carrying backpacks that may have contained the bombs, police said.

Within hours, gunfire was heard at MIT and the manhunt began.

Mayor, Obama praise police efforts

News of Tsarnaev’s arrest drew widespread praise for the police officers and agencies involved in the case.

“I feel so good about this…I’m so happy,” Boston Mayor Tom Menino told reporters, urging everyone to remember the victims of the marathon attacks.

President Barack Obama also praised the police, emergency and intelligence response. He referred to the suspects as “terrorists.”

“The families of those killed so senselessly deserve answers,” he said Friday night.

Obama said there are still “many unanswered questions” and investigators will work to determine how two young men who lived and studied in the U.S. for so long became suspects in one of the country’s worst public attacks.

With files from Andy Johnson