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Police officers return to the Cambridge Police headquarters in East Cambridge after Friday’s manhunt was over.

A steady stream of visitors paid tribute to MIT police officer Sean Collier in front of Building 32 on Saturday April 20. Collier was slain near this location on April 18 in his police cruiser.

A sign for Officer Collier adorns the window of the MIT Police Headquarters on Vassar Street.

Hundreds of paper cranes and origami flowers were draped on the MIT police cruiser in the Stata Center in honor of Officer Sean Collier.

A makeshift memorial to MIT Police Officer Sean Collier was erected by a steady stream of visitors in front of Building 32 on Friday, April 19, 2013.

A large sign from the women of McCormick Hall joins many others at MIT Police Headquarters in thanking and remembering Officer Collier.

The Green Building at MIT was lit in tribute to MIT police officer Sean Collier on the night of April 19, 2013.

Residents of Next House left hand prints across a poster thanking the MIT Police Saturday night. Residents also wrote individual cards which were then delivered.

Students in Simmons Hall printed a gigantic MIT Police badge across hundreds of pieces of 8.5”x11” paper. The sheets were assembled and hung in Simmons Dining.

Hackers hung a banner inside Lobby 7 in memory of fallen MIT police officer Sean Collier.

Hackers placed the MIT Police badge on the façade of Building 10 in memory of Officer Sean Collier.

A large American flag was raised behind the stage at Sean Collier’s memorial by two firetruck ladders.

Members of the Irish American Police Officers Association of Massachusetts play on the bagpipes in honor of Sean Collier.

MIT police officers place the casket of their fallen colleague down.

Police shut down Mass Ave. around 8am to all but pedestrian and bike traffic in preparation for the memorial for Sean Collier.

On Friday, April 19, following news that the second suspect in Monday’s bombings had been captured, people, many students, gathered in the Boston Common to celebrate.

Mechanical Engineering Professor Alex H. Slocum ’82 arrives for the memorial service for MIT police officer Sean A. Collier.

A Massachusetts State Police helicopter flies over Briggs Field.

Vice President Joseph Biden spoke at Sean Collier’s memorial service on Wednesday.

Members of the MIT community joined law enforcement officials at the memorial for Sean Collier Wednesday on Briggs Field.

The Prudential Center was lit up on Monday evening for the Boston One Fund, the fund for the victims of the Boston Marathon Bombing.

The Green Building at MIT was lit with a ribbon in the colors of the Boston Marathon on the night of April 20 in tribute to victims of the bombing.

MIT police officer Kevin O’Connor paid tribute to fellow officer Sean Collier in front of Building 32 on Friday, April 19, 2013. Collier was killed near this location the previous night by the Marathon bombing suspects.

At 2:45 p.m. on Monday, April 22, members of the MIT community stood hand in hand forming a human chain along Vassar Street from the Collier memorial at Stata to the MIT Campus Police station for a statewide moment of...

Hackers placed the MIT Police badge on both the shoulder and chest of The Alchemist on April 22, 2013 in memory of Sean Collier.

Residents of East Campus’ Fifth East provided a donations bin during their party Saturday night. Proceeds went to the Jimmy Fund, of which Officer Collier was a longtime supporter.