REVERE – Police Chief Joseph Cafarelli will say it was a matter of timing, but the fact remains it was the Metro North SWAT Team, which he commands, along with MBTA Transit Police, who actually arrested alleged Boston Marathon bomber Dzhokhar Tsarnaev.”This whole operation was a massive amount of cooperation from every police department in the commonwealth and beyond,” Cafarelli said Monday. “We were in the right place at the right time.”The Metro North SWAT Team, comprising officers from Revere, Malden and Everett, was first called into service April 15 immediately following the explosions, Cafarelli said.The team did foot patrols of Boston’s Faneuil Hall, Government Center and City Hall, and Thursday was part of the presidential unit when President Barack Obama arrived for a prayer service to honor the victims of the bombing, he said.”Then about 2:30 or 3 a.m. Friday morning they requested our presence in Watertown,” Cafarelli said.The mission in Watertown was to conduct a methodical door-to-door search of every home within the perimeter that had been established by law enforcement officials, he said. He said it was typical and the residents were unfailingly patient and understanding but after 14 hours they were tired.”We were clearing the last house. We were ready to pack it in and the call came for the Boston SWAT team,” he said. “It came over the radio and we knew this was it.”Cafarelli said both Boston SWAT and Metro North raced their vehicles toward Franklin Street, where the suspect was said to be hiding in a boat in a backyard, and ran the last half mile wearing about 60 pounds of gear.”Boston was on one side and we took the other,” Cafarelli said. “By the time we were in place every agency was there.”Law enforcement officials eventually talked Tsarnaev out of hiding and when they called for an arrest team, Cafarelli and the MBTA officers were already in place at the end of the driveway.When asked if Tsarnaev came out of the boat on his own Cafarelli said simply, “We helped.”He was standing up in the back of the boat,” he explained. “He wasn’t responding to commands; we pulled him down off the boat.”Cafarelli said his first concern was that Tsarnaev was wearing a suicide vest, “so I opened him up like a trash bag.” He said he ripped Tsarnaev’s shirt and pants open and once he was satisfied he had no explosives on him he turned his attention to the boat. He said his second concern was that there was another body in the boat who might shoot them from behind.After he cleared the boat Cafarelli said he and his team cuffed Tsarnaev then handed him off to the medics and headed for home.”Our job was done and we didn’t have the mental capacity to do anything else,” he said. “Emotionally, physically and psychologically we were spent.”Cafarelli said he finally made it home at about 1 a.m., 23 hours after he first headed to Watertown. He caught a couple hours of sleep and then was up “and went for a good long run with the dog. It was good to just blow off some steam. I do a lot of thinking when I run.”Cafarelli wasn’t the only one who needed to decompress from the week’s events.Officer Joe Covino and his older brother, Sgt. Mike Mason, also found themselves in the middle of the bombing disaster, first as runners and second as first responders. Mason crossed the finish line just as one of the bombs exploded and he immediately jumped into the fray to help, Covino said. He said Mason grabbed wheelchairs from the finish line and belts and scarves from a nearby sports store where the windows had been blown out by the blast and began to help the injured.Later he would make his way back to his car and home where he showered, changed into his uniform and picked up his partner, an expert in explosives, a police dog named Walsh, and headed back to Boston, Covino said.”And we haven’t seen him since,” Cafarelli quipped.Along with working the crime scene, Mason and Walsh returned to Revere to help search the apartment of “a person of interes