Here's what you need to know about Sean Collier, the Massachusetts Institute of Technology campus cop who was shot to death by the suspected Boston Marathon bombers.
When he went hiking with the MIT Outing Club, he brought extra ear plugs for others to block out snoring in the crowded mountain cabin.
When his car got hit by a swerving vehicle, Collier immediately went to check if the other driver was injured.
Even those who barely knew him filled a tribute page set up Friday with memories of his easy laugh and ever-present smile, his desire to help others and his motivation to be a good police officer.
"He had a really great smile. I'll always remember that," Kristina Lozoya, a student volunteer with the MIT emergency medical service, told CNN. "He was always laughing. He loved his job."
Carin King, another volunteer with the service that runs the campus ambulance, told CNN that Collier "went out of his way" to get to know the student emergency medical technicians (EMTs).
"A few months ago he was on a call with me where the patient was very seriously ill," King related in an e-mail. "He followed up with the family and then stopped by our bunkroom to look for me every day for a week so he could let me know that our patient was now OK."
On Thursday night, when news emerged that an MIT officer had been shot, King sent Collier an e-mail "to make sure he was OK."
She never got an answer.
"I figured I was being overly cautious," King added. "It's truly a heartbreaking situation."
Such a connection reflected the 26-year-old Massachusetts native's approach to police work.
While his brother, Andrew, became a machinist in the engine department at Hendrick Motorsports, one of the major NASCAR racing teams, Sean followed a different path.
"Sean was one of these guys who really looked at police work as a calling," MIT Police Chief John DiFava said in a statement posted on the university website. "He was born to be a police officer."
Collier died a police officer, shot to death in his squad car on the MIT campus.
In a statement Friday, his family asked for privacy.
"We are heartbroken by the loss of our wonderful and caring son and brother," the statement said. "Our only solace is that Sean died bravely doing what he committed his life to -- serving and protecting others."
President Barack Obama praised Collier on Friday night following the conclusion of a daylong manhunt for the second of two marathon bombing suspects, saying he was a dedicated officer.
"We are grateful to him," Obama said.
Collier's killing and a subsequent carjacking nearby set off the search that paralyzed Boston.
The suspects were identified as brothers. One died following a shootout with police while the second was taken into custody, officials said.
After the blasts Monday near the finish line of the iconic road race, Collier's slaying further traumatized many in the MIT community who had gotten to know him during his 15 months on the job.
"The loss of Officer Collier is deeply painful to the entire MIT community," MIT President L. Rafael Reif said on the university website.
That included the MIT Outing Club, which organizes hiking and skiing excursions in the region. Collier, who was single, was an avid participant in trips to the mountains of New England that he hiked as a boy.
Club members described him as endlessly energetic and a joyous companion on the trail and around the campfire.
"We recall him bringing earplugs for an entire cabin full of people, going out of his way to give people rides, offering help for bike or any other problems," said a statement on a tribute page set up at MIT.