(CNN) -- 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."
Boston bombing suspect Dzhokhar Tsarnaev is detained by officers on Friday, April 19. After a car chase and shootout with police, one suspect in the Boston Marathon bombing, Tamerlan Tsarnaev, was shot and killed by police early Friday, and his brother and second suspect, Dzhokhar Tsarnaev, was taken into custody Friday night. The two men are suspects in the bombings at the Boston Marathon on April 15, that killed three people and wounded at least 170. See all photography related to the Boston bombings.
Photos: Manhunt for Boston bombers
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 27-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.
"He made a point of getting to know students, asking them about details of their lives, enthusiastically sharing his own experiences. He brightened the lives of all of us, and words cannot describe the loss we feel."
Fellow club member Andrew Ding told of the car crash during a drive to New Hampshire, describing how Collier showed no hint of anger or exasperation over the damage to his vehicle.
"Sean was the first out of our car to go check and see if the (other driver) was OK," Ding wrote in an email to CNN, adding that "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."
Such awareness and devotion were evident in college, said Kristen Kuehnle, who chairs the department of criminal justice at Salem State University, where Collier graduated with honors in 2009 as a criminal justice major.
Kuehnle remembered that Collier got an 'A' in the "Women in Criminal Justice" class she taught, recalling him as "bright" and well-rounded with a "great sense of humor that you really need."
"When you're graduating with honors, you've demonstrated ability to be thoughtful and look at all perspectives," she said.
Describing Collier as a model candidate for police work, she said he had "the vision that we are looking for in our students."
"He always wanted to be a police officer," Kuehnle said. "That was pretty clear, but it wasn't like the whistles and bells and toys. It was about really wanting to make a difference and being good at what you do."
That's the impression he left on those who knew him at MIT.
"Sean is not the stereotypical cop who is kind of intimidating, but rather a friendly and down-to-earth kind of guy that you would want to be friends with," David Hou, an MIT sophomore, told CNN.
To Ding, Collier was "the kind of guy you'd ask to watch your wallet."
Ben Artin, another EMS volunteer, told how Collier proposed arranging a social event to help broaden the relationship between the campus police and the emergency service workers.
"Sean was rare in the degree to which, while working for MIT PD, he wanted to socially engage with the students," Artin wrote to CNN, adding that "I hope that we follow through on this proposal as we heal."
CNN's Sally Holland contributed to this report.
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Special imaging techniques employed by Massachusetts State Police reveal Boston Marathon bombing suspect Dzhokhar Tsarnaev hiding in a boat in a backyard in Watertown on April 19.
Dzhokhar Tsarnaev gets out of the boat he was hiding in outside of a home in Watertown, as seen in a surveillance video still.
An ambulance carries Boston Marathon bombing suspect Dzhokhar Tsarnaev, 19, from the scene after he was apprehended in Watertown, Massachusetts, on April 19.
Police SWAT teams leave the area after apprehending the suspect in a yard where he was hiding in a dry-docked boat on April 19.
Residents flee from an area where a suspect was hiding on Franklin Street on April 19.
SWAT team members run toward a police assault on a house as gunfire erupts on April 19.
People react while watching police respond to reported gunfire on April 19.
SWAT team members move down residential streets as they perform door-to-door searches in Watertown, Massachusetts, on April 19.
A U.S. military helicopter lands behind Watertown Mall as law enforcement agencies continue to search for the 19-year-old bombing suspect on Friday.
SWAT teams prepare to enter a home as they continue the door-to-door search.
U.S. President Barack Obama meets with members of his national security team in the Situation Room of the White House on April 19 to discuss developments in the Boston bombings investigation.
SWAT team members line a residential street in Watertown, Massachusetts, as the manhunt continues on Friday.
A man watches from the window of a home as a SWAT team member keeps watch on Friday, in Watertown, Massachusetts.
Police to continue to the door-to-door search on Francis Street in Watertown, Massachusetts, on Friday.
Law enforcement officers place themselves in an overhead position on Arsenal Street as the search continues on April 19.
Law enforcement officers react to what was initially thought to be a threatening suspect on Arsenal Street on April 19.
A police SWAT team searches houses on April 19 for the second suspect.
SWAT teams searches homes along Winsor Avenue in Watertown on April 19.
A Massachusetts state trooper watches other troopers line up at Watertown Mall as the manhunt for the second suspect continues in Watertown on Friday.
Police continue the ongoing manhunt for the second suspect on Williow Avenue in Watertown on Friday.
A Watertown police vehicle with bullet holes in its body and a shattered windshield is towed out of the search area on April 19 in Watertown, Massachusetts.
A Massachusetts State Police officer checks the bag of a cyclist amid heightened security on Friday in Watertown.
Katia Costa looks out her window as police continue the manhunt on Nichols Avenue in Watertown on Friday.
Ruslan Tsarni, uncle of the Boston terror suspects, told CNN affiliate WBZ that Tamerlan "got what he deserved" in an interview outside his home in Montgomery Village, Maryland, on Friday.
A woman is questioned by Cambridge police and other law enforcement agencies Friday near the home of the second suspect in Cambridge, Massachusetts. A Massachusetts Institute of Technology campus police officer was shot and killed late Thursday night at the school's campus in Cambridge. A short time later, police reported exchanging gunfire with alleged carjackers in nearby Watertown.
SWAT teams move into position at the intersection of Nichols and Melendy avenues in Watertown, Massachusetts, on Friday.
SWAT teams gather at the intersection of Nichols and Melendy avenues in Watertown while searching for the remaining suspect on Friday.
Onlookers take pictures while SWAT team members look around on Friday.
Massachusetts Gov. Deval Patrick, left, speaks to the media at a shopping mall on the perimeter of a locked-down area during the search on Friday.
Metro SWAT members hang off the back of a truck during the search on Friday.
SWAT officers check a door with guns ready on Friday.
Officers patrol Watertown on Friday.
The aftermath of the shootout that police said involved the two suspects in Watertown early Friday.
Police with guns drawn search for a suspect on Friday in Watertown, Massachusetts.
A police officer runs with his gun drawn on Friday.
Boston Police gather in the parking lot in front of a Best Buy store near the Watertown Mall on Friday.
Boston Police Commissioner Edward Davis speaks during a media briefing in the parking lot of the Watertown Mall on Friday.
Boston police gather in front of a Best Buy on Friday.
Police stop cars at School and Walnut streets on Friday.
A Massachusetts state trooper checks a building along Mount Auburn Street as police search neighborhoods in Watertown.
Police search neighborhoods yard by yard on Friday.
Police convene on School and Walnut streets on Friday.
A police officer talks to a driver at a checkpoint in Watertown, Massachusetts.
Police officers keep a man on the ground in Watertown on Friday. See all photography related to the Boston bombings.
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