PITTSFIELD -- Former Boston Police Commissioner Edward Davis III offered an insider's view of the Boston Marathon bombings and its aftermath during a talk Friday that drew about 500 people to the Colonial Theatre.

Davis gave the sixth annual Mona Sherman Memorial Lecture, which is associated with the Osher Lifelong Learning Institute at Berkshire Community College.

After showing news film clips of the April 15, 2013, bombings near the marathon finish line on Boylston Street in Boston and the massive five-day search for the bombers, Davis said he took personally that "my city was ruthlessly attacked."

In the coming months before the pending trial of bombing suspect Dzhokhar Tsarnaev, Davis predicted more revelations will emerge in what became "the most complex investigation ever to come across the desk of the Boston Police Department."

He noted news of the arrest this week of a Quincy man for allegedly assisting Tsarnaev and his brother, Tamerlan Tsarnaev, who died from wounds in a firefight with police. Davis said his sense is that there was a larger network of individuals or terrorist groups involved in the attack, which resulted in the deaths of three and serious or permanent injuries, notably loss of limbs, for many others.

"These were very powerful bombs," Davis said he realized the moment he came to the scene. Two of the three victims killed in the blasts still lay on the ground, he said, and there was a great deal of blood in the street.

"I immediately felt the shrapnel crunching under my feet," he said, which told him that the bombs contained BBs and copper tacks, which are packed into bombs in order to rip flesh and inflict injuries over a wide area.

One of the bombs broke windows in the upper floors of nearby buildings, he said, adding that this is just one reason he believes the suspects were particularly ruthless, not young immigrant men who might have felt alienated from American culture.

Davis said he was standing with his wife near one of the bomb sites, but he had returned home after the winners and the main body of the marathon runners had crossed the finish line and been honored by Gov. Deval Patrick. He said he and others in charge of providing security for the event -- including 842 BPD officers along Boylston Street -- had begun to believe the most dangerous moments for a terror attack had passed. "I felt a sigh of relief," he said.

Terrorists are known to target the maximum number of people at an event and strike when the media is focused on the scene. "They want to hit a place where they can kill a lot of people, in full view of the world," he said.

But Davis said this attack occurred shortly after that moment.

As the Boston Marathon is "a perfect place for a terrorist to hit," police and emergency personnel had done extensive prior planning, Davis said, including cooperative exercises with medical and other personnel. Although they couldn't prevent the attack, the response to the bombings was immediate and inspiring, he said.

"One big lesson," he said, "is that you have to involve all the players before the bombs go off. You can't establish relationships during a crisis."

Police officers, swat teams and state and federal law enforcement officials were able to communicate well, even during such a chaotic scene as a hospital when police arrived to check for possible wounded bombing suspects.

There were 42 code red evacuees, or those with life-threatening injuries, Davis said, and they were all moved within 18 minutes. Sometimes quick decisions had to be made, such as whether to wait for an ambulance or take someone in another vehicle, but the correct choices were made, he said.

Illustrating the overwhelming nature of the bombings and the 102-hour manhunt that followed leading to one suspect's death and the other's capture, Davis said that at first he did not have enough officers to even secure the huge crime scene.

But he soon had an offer of 1,000 National Guard troops to assist, and 1,000 state troopers eventually became involved in the investigation and the arrest. Cooperation among the FBI, DEA, state and local police was excellent and extensive, he said.

Davis also described from his perspective key moments in the intense search for those responsible, including involvement in difficult decisions made under worldwide media scrutiny -- such as whether to lock down city streets after the first shootout with police or when to release photos of apparent suspects captured on surveillance cameras.

"When I saw the tape, I knew we had these guys, if they were dumb enough to stay around," he said, but the effects of releasing the photos and tipping the suspects off versus a lower-profile search first had to be weighed.

Davis also praised the response of average citizens of Boston, such as the man who noticed Dzhokhar Tsarnaev hiding in a boat parked near his house, which led to the arrest.

The public might have come to think another major attack would not occur so long after Sept. 11, 2001, but Davis said public safety personnel kept reminding themselves that it could happen again.

"This shook the nation; it had a major effect on the entire country," he said.

Davis left his job in Boston in September 2013 and earlier this year joined WBZ-TV News in Boston as a security analyst. He also is an assisting fellow at the John F. Kennedy School of Government at Harvard.

He began a 36-year career in law enforcement with the Lowell Police Department in 1978 and served in the Boston commissioner's post from 2006-13.

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