Thousands of students and officers are attending a memorial service for the officer killed in a shootout following the Boston Marathon bombings.

Sean Collier had worked for the Massachusetts Institute of Technology police for over a year and was popular on campus.

US Vice President Joe Biden is expected to speak at the service.

"Sean was one of these guys who really looked at police work as a calling", said MIT Police Chief John DiFava. "He was born to be a police officer".

DiFava said Collier was highly involved with the MIT student population. "In a very short period of time, it was remarkable how engaged he was with students" DiFava added.

A funeral service for another victim of the Boston Marathon bombings - 29-year-old Krystle Campbell - took place on Monday.