A year ago Friday, the tragedy of the Boston Marathon bombing on Boylston Street three days earlier crossed the Charles River into the city of Cambridge.

It was early in the evening on April 18 when the FBI released photos of the alleged bombers — brothers Tamerlan and Dzhokhar Tsarnaev -- shaking those who knew them as neighbors in Cambridge and those who remembered Dzhokhar as a high school student not long before.

A few hours later, the MIT campus shook as well.

A 'False Security' Before An Officer Falls

"The word was out regarding the suspects now. We knew how they looked like, and we knew they lived in the city of Cambridge at one point," said Clarence Henniger, a sergeant with MIT police, recalling patrolling campus that evening.

"So our alert basis was not as high because the feds were all over the city of Cambridge, to some degree, knowing that they lived there," Henniger said. "It was still not really affecting us directly in a sense. We still had this false security of MIT campus. We felt the threat here in Cambridge was gone."

Sean Collier (MIT)

We now know the threat was not gone, as MIT Police Officer Sean Collier, working his regular beat, was shot in his cruiser, allegedly by the bombing suspects.

Henniger had driven by Collier only moments before Collier failed to respond to calls from a dispatcher. Henniger went back to check on him. This time, out of his car, he approached Collier's cruiser.

"And as I came to the front, up to this point, I don't know how long I may have frozen. I could not believe what I was looking at," Henniger recalled. He was the first to reach Collier, who had been shot several times and was seriously wounded.

"At that point I backed away, and I realized what was going on. I just got on my radio and I said, 'Officer down, officer down. Get me medical, get me back-up. Officer down.' "

Across Cambridge, Shock, Disbelief and Confusion Settled In

Right around the same time, across Cambridge there was shock, disbelief and confusion of a different kind settling in as word of the likely identity of the suspects reached Peter Payack, Dzhokhar Tsarnaev's former wrestling coach at Cambridge Rindge and Latin High School.

"My son called me and he said, 'Dad, that's Dzhokhar.' And I said, 'That's Dzhokhar?' And I couldn't even talk, it was like a bullet went through my chest because Dzhokhar is one of my closest wrestlers," Payack recalled. "And it was just like, it shattered, it was like I got shot in the heart. I couldn't talk. It was like one of these things that you can't believe it's really your guy. It's Dzhokhar? And from that point on, it's like my life took a different path."

In the months since, Payack has said he thought Dzhokhar was not a kid who would get in trouble.

"It was just like, come on Dzhokhar, what were you thinking?" he said. "It was just like a betrayal to his community, to his high school, to his friends, his coaches. It was like a betrayal to all of us. A betrayal to the whole idea that, hey, we're all one family. We always say, we're one family in Cambridge."

Payack was on the street in Watertown after the capture and watched the ambulance with Dzhokhar inside go by. He was also there months later, trying to get into the courthouse for Dzhokhar's arraignment, but was turned away with other spectators.

These interviews were conducted by Jayne Guberman as part of the WBUR Oral History Project, a collaboration with Northeastern University’s “Our Marathon: Boston Bombing Digital Archive.”