MIT has identified the police officer killed in the line of duty on Thursday evening as Patrol Officer Sean A. Collier, 27, of Somerville, Mass.Collier had served as a member of the MIT Police since Jan. 9, 2012, following service as a civilian employee with the Somerville Police Department. He was single and a native of Wilmington, Mass.“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.”Collier was shot Thursday evening following an altercation at the corner of Vassar Street and Main Street in Cambridge, roughly between Building 32 (Stata Center) and Building 76 (David H. Koch Institute for Integrative Cancer Research) on the MIT campus. He was transported to Massachusetts General Hospital, where he was pronounced dead.The MIT Police, Cambridge Police Department and Massachusetts State Police are continuing their investigation of the circumstances surrounding Collier’s death.“The loss of Officer Collier is deeply painful to the entire MIT community,” MIT President L. Rafael Reif said. “Our thoughts today are with his family, his friends, his colleagues on our police force and, by all accounts, the many other members of our community who knew him. This is a senseless and tragic loss.”“The MIT Police serve all of us at the Institute with great dignity, honor and dedication,” said Israel Ruiz, MIT’s executive vice president and treasurer. “Everyone here — those who knew Officer Collier, and those who did not — are devastated by the events that transpired on our campus last night. We will never forget the seriousness with which he took his role protecting MIT and those of us who consider it home.”DiFava said Collier was highly involved with MIT’s student population. “In a very short period of time, it was remarkable how engaged he was with students,” DiFava said.“He wanted to get to know students — he wanted to understand us,” senior Michele Pratusevich said. “And he did it; he knew which students he was protecting every day when he came to work. By getting to know students, by talking to us, by sharing memories with us, by hiking with us, by dancing with us, by listening to music with us, he knew his community. He loved us, and we loved him.”Maddie Hickman ’11 recalled Collier’s frequent stops by MIT’s student center while on his shift — and his dancing of the Lindy Hop.“At first, some of the dancers were nervous at the ‘police presence’ in the room, but Sean made friends quickly,” she said. “In the spirit of trying new things, he even started taking swing-dancing lessons in his time off, so he could participate in future dances ‘without being embarrassed,’ as he said.”Dozens of other students and alumni who met Collier in his 15 months at MIT described him as “dedicated,” “cheerful,” “personable,” “charming” and “kind.” Many encountered him through his involvement with MIT-EMS, the Institute’s ambulance service — which transported the wounded officer to Massachusetts General Hospital last evening.“Many on campus knew him because he was just so friendly,” junior Max Tang recalled. “I had known of him for many months before having the pleasure of meeting him. … He was always smiling, always had a funny story to tell, and he would always remember what I was up to last time we spoke and would ask about it. … He truly was an asset to our campus.”“He inherently cared about this campus, and the people in this community,” Lawrence Wong, a graduate student in aerospace engineering, said. Sophomore David Hou described Collier as “a friendly and down-to-earth kind of guy that you would want to be friends with.”The young officer, MIT senior Noel Morales said, was a regular presence at student events — and one who would always introduce himself to students, ask their names, and crack jokes. “He was always really fun to hang out with,” Morales said.Even students who had only just met Collier felt drawn to him.“I met Sean just a week ago,” sophomore Jennifer Plotkin said. “After the events at the Marathon on Monday, Sean Facebook-messaged me to tell me that he was glad I was OK. … He was extremely kind, caring and a joy to be around.”“In the short time I knew him it was obvious that Sean cared deeply about his job, his friends and family, and anyone around him, even if he had just met them,” MIT-EMS member Kat Goldsmith said. “He assisted and protected me even before he knew my name, even going out of his way to follow my all-female squad on calls (even when he knew we could take care of ourselves). That was just the kind of person he was — quick to go out of his way to help others, make a joke and smile.”Collier was also active with the MIT Outing Club (MITOC), joining students in hiking — especially winter hiking.“During one hike, we tried to make it ‘retro-MITOC-themed,’ including yodeling,” Pratusevich recalled. “Sean claimed he wasn’t much of a singer, but was one of the first to try his hand at the elusive art of yodeling. Hearing his deep voice crack over those yodels definitely made that hike (we didn't reach the top) one of the more fun hikes I’ve been on. He was eager to strut his plaid flannel, yodel off the sides of a mountain, enjoy eating his chocolate and pepperoni, and be happy and cheerful even with our exceedingly slow pace.”Others were amazed by Collier’s rapid embrace of winter hiking in New Hampshire’s White Mountains — home to some of the nation’s most brutal weather.“Sean was a MITOC all-star,” mechanical engineering graduate student Matthew Gilbertson ’08 said. “In my nine years with MITOC, I have never seen a star rise as fast as Sean’s.”“The thing that impressed me about Sean was how enthusiastically he took the plunge into winter hiking, how quickly he mastered it, and how rapidly he made friends,” Gilbertson added. “Sean’s first big winter hike was in January, and just a few weeks later, he was already climbing Mount Washington in winter — one of the toughest outdoor feats in the eastern United States.”“He was the kind of person who would willingly offer help, even at inconvenience to himself, without having to be asked,” MITOC member Andrew Ding added. “It’s easy to understand why he became a police officer. He gave me the strong impression he had an altruist’s heart.”Ding said that a few months ago, he and Collier were involved in a car accident while driving to the White Mountains for a MITOC trip. “Sean was the first out of our car to go check and see if the [other driver] was OK,” Ding said. “It would be exceedingly difficult to imagine him not stepping up and doing the right thing when he had the chance, which unfortunately he did last night.”Collier’s family has requested that gifts in his memory go to The Jimmy Fund . MIT has created a Sean A. Collier Memorial Fund that will support a Collier Medal — to be awarded to individuals who demonstrate Collier’s values — and other causes.