Wells had not heard. His Monday had been dominated by the investigation into the fatal stabbing of a 22-year-old resident the previous night. It was the town’s first homicide of the year, and the killer was on the loose.

But within an hour and a half of the deadly terrorist attack near the Marathon finish line, Wells and 10 of the department’s tactically trained officers, including a bomb-sniffing K9 unit, had rushed to the expansive crime scene in Copley Square and to other areas of the city that needed to be secured amid the chaos, including Faneuil Hall and hospitals.

“It was the last thing I thought I was going to be doing last week, I can tell you that,” Wells said.

Milton’s contingent was among 100 specially trained officers that had been mobilized to aid Boston Police investigators through the Metropolitan Law Enforcement Council , a consortium of 42 regional police and sheriff departments.

And they were among the hundreds of other police officers from communities across the state who descended upon the city, working 12- to 18-hour shifts at a time, on the heels of the twin bombings that killed three and wounded more than 260, and finally to Watertown late last Thursday and early Friday, where a massive manhunt for the two suspects culminated with the death of one and the apprehension of the other.

With the focus now shifting toward the recovery of those injured in the bombings and the federal case against 19-year-old Dzhokhar Tsarnaev, law enforcement officials in communities around Boston are reflecting upon the week that was, and getting ready to tally up the financial toll on their departments.

Since being alerted to the bombings, Wells split 12-hour shifts between Boston and Milton up until 5 p.m. Saturday when Boston Police officially closed the mutual aid operation.

“There was a lot of handshaking, a lot of thanks,” Wells said. “You realized when you left there, you just witnessed an event that most people could never imagine.”

From the bombings on Patriots Day to last Thursday, when President Obama and Michelle Obama arrived in Boston for an interfaith service and later visited the wounded in hospitals, area police departments staffed Boston with a multitude of officers and special units working at least 12-hour shifts, most of it overtime, area chiefs said.

For Obama’s visit alone, the Massachusetts Major City Chiefs , an organization for departments staffed with at least 75 police officers, deployed 330 officers from various communities at the request of Boston Police Commissioner Edward Davis, said Brian Kyes, Chelsea’s police chief and the group’s vice president.

With Obama declaring a state of emergency, some of those costs are expected be covered by Federal Emergency Management Agency funds. A spokesman for the Massachusetts Emergency Management Agency said the agency will eventually have a complete list of police departments that assisted in the bombing aftermath and manhunt, but that could take weeks or months. A spokeswoman for the FBI’s Boston division indicated that exact numbers could be hard to track since many police officers may have volunteered to help.

Arlington Police Chief Frederick Ryan, who sent 30 officers to Boston and then Watertown, including some trained in SWAT operations and others on motorcycles to patrol streets, hasn’t had a moment yet to calculate the total cost.

But he said that during the response operation, cost was never part of the equation, particularly when it became clear Thursday night that the two suspects had killed MIT Police Officer Sean Collier and seriously wounded MBTA Officer Richard Donohue Jr.

He said 30 off-duty officers had asked to be sent to Watertown to help with the manhunt. In their thoughts, he said, was Krystle Campbell, one of the victims killed by the bomb explosions, who had recently moved to Arlington.

“I think the fact that one of the deceased victims lived and worked in Arlington provided an additional motivation for our police officers,” Ryan said.