Police on Thursday identified the man they say carried out a murder-suicide that took the life of an engineering professor at UCLA.

The shooter was Mainak Sarkar, said Officer Jenny Houser, a city police spokeswoman. Sarkar is listed on a UCLA website as a member of a computational biomechanics research group run by the victim, a professor of biomechanical engineering.

The shooting Wednesday brought a massive police response and widespread fear of an active shooter among tens of thousands of people at the university. Now fear has shifted to sadness as many lament the death of a professor who worked on computer models of the human heart who was also a doting father who coached his young son’s baseball team.

Bill Klug, a professor of mechanical engineering, was gunned down in an engineering building office Wednesday, according to a law enforcement official with knowledge of the investigation but not authorized to publicly discuss it.

Finding the gunman’s motive in killing Klug will be foremost in the investigation as it continues Thursday.

Classes at the University of California, Los Angeles campus will resume Thursday for most of the school, and on Monday for the engineering department, whose students and faculty were coming to grips with his loss.

“Bill was an absolutely wonderful man, just the nicest guy you would ever want to meet,” said a collaborator, UCLA Professor Alan Garfinkel. “Devoted family man, superb mentor and teacher to so many students. He was my close colleague and friend. Our research together was to build a computer model of the heart, a 50 million variable ‘virtual heart’ that could be used to test drugs.”

Peter Gianusso, who headed the El Segundo Little League where Klug coached, said he “exemplified what Little League was all about: character, courage and loyalty.”

“He had a special relationship with his son through baseball, was a great coach, spent countless hours on the field with the boys and girls of El Segundo Little League,” Gianusso said.

The initial reports from the scene set off widespread fears of an attempted mass shooting on campus, bringing a response of hundreds of heavily armed officers who swarmed the campus.

Groups of officers stormed into buildings that had been locked down and cleared hallways as police helicopters hovered overhead.

Advised by university text alerts to turn out the lights and lock the doors where they were, many students let friends and family know they were safe in social media posts. Some described frantic evacuation scenes, while others wrote that their doors weren’t locking and posted photos of photocopiers and foosball tables they used as barricades.

After about two hours, city Police Chief Charlie Beck said it was a murder-suicide and declared the threat over. Two men were dead, and authorities found a gun and what might be a suicide note, he said.

It was the week before final exams at UCLA, whose 43,000 students make it the largest campus in the University of California system.

Those locked down inside classrooms described a nervous calm. Some said they had to rig the doors closed with whatever was at hand because they would not lock.

Umar Rehman, 21, was in a math sciences classroom adjacent to Engineering IV, the building where the shooting took place. The buildings are connected by walkway bridges near the center of the 419-acre campus.

“We kept our eye on the door. We knew that somebody eventually could come,” he said, acknowledging the terror he felt.

The door would not lock and those in the room devised a plan to hold it closed using a belt and crowbar, and demand ID from anyone who tried to get in.

Scott Waugh, an executive vice chancellor and provost, said the university would look into concerns about doors that would not lock.

One student who spent hours sheltering in a building did the same thing almost exactly two years ago when he was locked down in a dorm at UC Santa Barbara during a shooting rampage in the surrounding neighborhood that left six students dead and wounded 13 people.

Jeremy Peschard, 21, said it was “scary” and “eerily similar” but also that having been through the feeling of crisis before left him almost numb.

“I just felt a little bit less shocked, a little bit less taken aback by the reality of an active shooter on a college campus,” he told The Associated Press in an email. “Because I feel like this is the day and age we’re living in, that college campus shootings have genuinely become a normalized threat, almost like a natural disaster, except this type of destruction isn’t natural. It’s just really sad.”

UCLA’s commencement ceremonies and end-of-year events will now include mourning Klug, who was a devout Christian and a regular figure in organizing campus spiritual life.

In 2012, according to the campus website, he moderated a forum that his family and friends might find useful now. Its title: “Does God Care?: Seeking the Meaning of Life in the Midst of Suffering and Death.”

(AP)