SOMERVILLE, Mass. – The Massachusetts Institute of Technology police officer slain just days after the Boston Marathon bombing has been posthumously sworn in as a Somerville officer.

Authorities allege the marathon bombing suspects shot and killed Sean Collier on April 18 to get his gun.

Additional Photos

William Kellehar, grandfather of Sean Collier and Pat Kelleher, aunt of Sean Collier, arrive at the ceremony for Sean Collier, the MIT police officer who was slain just days after the Boston Marathon, Thursday, Aug. 22, 2013 in Somerville, Mass. Sean Collier, the Massachusetts Institute of Technology police officer slain just days after the Boston Marathon bombing has been posthumously sworn in as a Somerville officer. (AP Photo/The Boston Globe, Matthew J. Lee)

In this 2010 photo, Richard Donohue Jr., left, and Sean Collier pose for a photo at their graduation from the Municipal Police Officers' Academy. Collier, a Massachusetts Institute of Technology Police Officer, was fatally shot on the MIT campus, and transit police officer Donohue was shot and critically wounded, both allegedly by the Boston Marathon bombing suspect on the night of his capture. The Associated Press

Collier’s brother spoke for his family at a ceremony at Somerville City Hall Thursday night. Boston’s WFXT-TV Fox25 reports he asked those who attended to be “Collier strong,” echoing the “Boston Strong” bombing recovery theme.

Among those attending was MBTA officer Richard Donohue, a friend of Collier’s wounded in a police shootout with the bombing suspects.

Collier was assigned badge number 310, which was then retired in his honor.

The 27-year-old had accepted a position in Somerville before he was killed and was just weeks away from starting his new job.

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