Some 15,000 people attended the outdoor service for 27-year-old Sean Collier, including hundreds of fellow officers. Vice President Joe Biden joined thousands of students, faculty and staff, and law enforcement officials from across the nation at Briggs Field.
Biden called the bothers suspected in the bombings and Collier's killing "two twisted, perverted, cowardly, knock-off jihadis."
"We are grieving, but we are not bending. We will not yield to fear," Biden said. "It infuriates them that we refuse to bend, refuse to change, refuse to bend to fear."
Investigators said they believe brothers Tamerlan and Dzhokhar Tsarnaev shot Collier to get his gun, but failed because of his safety holster.
The area near the Boston Marathon finish line reopened to the general public in the morning. Boylston Street had been closed since the April 15 bombings.
Traffic was allowed to flow all the way through for the first time since the twin blasts that killed three spectators and sent more than 260 people to the hospital.
Suspected bomber Dzhokhar Tsarnaev will continue to be interrogated inside his hospital room. The 19-year-old's condition was upgraded to fair.
Dzhokhar Tsarnaev was captured Friday following a massive manhunt that shut down the city of Boston. He was discovered hiding in a boat covered by a tarp, which was parked on the property of a home in nearby town of Watertown.
Two U.S. officials said Tsarnaev was unarmed when police captured him hiding inside the boat. Authorities originally said they had exchanged gunfire with him for more than one hour Friday evening before they were able to subdue him.
The officials said no gun was found in the boat. Boston Police Commissioner Ed Davis said earlier that shots were fired from inside the boat.
Tsarnaev's older brother, 26-year-old Tamerlan, was killed in a shootout with police hours earlier. Investigators said they recovered one 9 mm handgun from that scene. His body remains at the medical examiner's office, still unclaimed by next of kin.
There's increasing scrutiny over how the government tracked Tamerlan Tsarnaev when he traveled to Russia last year. After a closed-door briefing on Capitol Hill with the FBI and other law enforcement officials Tuesday, authorities said it doesn't appear that anyone dropped the ball, but communication among agencies and even within the same agency may be at issue.
Investigators say the bombs were built with parts found at any typical hardware store.
More than two months before the bombings, older brother Tamerlan Tsarnaev bought two re-loadable mortar-style fireworks from a New Hampshire store. Employees say he was looking for one thing in particular.
"He just wanted the biggest, loudest stuff we had in the store, pretty much run-of-the-mill questions that we get asked by every customer who walks through the store," said Megan Kearn, the assistant manager at Phantom Fireworks.
According to the FBI, Dzhokhar Tsarnaev told agents that the U.S. wars in Afghanistan and Iraq were motivating factors behind their attack.
However, the suspects' mother said her boys were set up, and her family is being targeted because of their religion. She is headed for a second day of FBI interviews in Russia. ABC News has learned that she has an outstanding warrant for shoplifting in the U.S. If she returns to the U.S. to claim her older son's body from the coroner or to visit her younger son in the hospital, she could be arrested.
The mother and father of the two suspects say they will fly to the U.S. on Thursday and will cooperate with the investigation. They want to bring the body of their older son back to Russia. They were interviewed by the FBI in Russia Wednesday.
As of Wednesday morning, a central fund set up to help victims of the bombings has raised more than $20 million. Those victims and their families directly affected by the attack could see compensation as early as June 30.
Meantime, the Watertown man who discovered suspect No. 2 hiding in his boat is speaking out. David Henneberry says he doesn't consider himself a hero. Online donation sites have been created to help Henneberry fix or replace his beloved boat.
The Associated Press contributed to this report.