This is the fourth of four stories in an ongoing series.

Minutes after news went out that Boston Marathon bombing suspect Dzhokhar Tsarnaev had been flushed out of the boat where he was hiding, Watertown exhaled.

“Go Watertown!” crowds shouted.

Police forces from Winchester, Westford, Woburn, the National Guard, Billerica, the Massachusetts State Police, Watertown, Boston, Cambridge and elsewhere were celebrated like war heroes. And that evening, Watertown Police Chief Ed Deveau hailed the 18-hour manhunt as a model for the nation.

However, six months later, Deveau is more circumspect, preferring to view the Watertown shootout, lockdown and arrest as a case study rather than a model.

"Some of the local colleges have already been reaching out to people to find the lessons learned," he said. "I know the state is in the process of putting together the beginnings of an after-action report, so we can look at that and have it professionally looked at. That's going to take a while, because there are so many things that happened, and so many different agencies. You can't do this and just clean up afterwards and just wait for the next time. We have to study it. We have to look at it."

Still, Deveau says that if there is one example of excellence that can be gleaned from the 18 hours that began with the killing of MIT Police Officer Sean Collier in Cambridge, it is the way that law enforcement banded together to track down the suspects.

"Boston, Cambridge, the State Police, the surrounding communities, and the federal agencies that were able to come in and support us — no one, no one, worked outside of the group," he said. "That day, all law enforcement worked together in just an incredible way. It'll always be the highlight of my career, the proudest I've ever been."

And exactly who was in charge that night?

"Nobody," Deveau said. "We literally just sat around a table and made all the decisions collectively. Whether it was 5 a.m. with [Boston Mayor Tom Menino and Gov. Deval Patrick] on the phone, and we tossed around the ideas of what we were going to do — shut down just Watertown, or are we going to make it a bigger area? And we really went around the table and came to a group decision, and that's what followed the whole day. So, There was no one that had any bigger voice than the person sitting beside him."

Cambridge Police Commissioner Robert Haas explains how the command structure at the Arsenal Mall came together that night.

"It was a combination between the Boston Police and the State Police that basically had taken control," Haas said. "As you can imagine, Watertown had five, six officer working, and the enormity of that incident really overwhelmed Watertown Police. And so it was really the assistance of State Police and Boston that we actually started to develop that whole plan around how we were going to do the whole search and going through it. Chief Deveau was there the entire time. Chief Davis was there the entire time. I was there the entire time. So we worked together, we stayed together, we talked together."

Nevertheless, Hass says self deployment by officers to Watertown from various cities and towns was a concern. There’s a lesson here, he says.

"The moments after the marathon, they couldn't get enough police officers to respond," he said. "And the fact that they did respond the way they did helped them secure a number of scenes. As you can imagine, the chaos that day, thinking about what took place at the finish line — the Watertown incident was different, in a sense, because it was very prolonged. It went on for hours and hours, and actually trying to get control of the number of people, the mass of people that showed up, proved to be a challenge for the people who are trying to organize that event."

Police are also studying the many incidents of bullets fired into the homes of east Watertown residents. As we reported earlier, one bullet from the direction of police came within a few inches of hitting a bed where a toddler was sleeping.

Another went through a chair where a man had been sitting just moments earlier.

"It had penetrated the wall and the desk chair, clean through," the man said.

Watertown residents are also reflecting on the lessons of the violent standoff. Jeffrey Ryan and Mike Doucette live in houses 12 yards apart at the intersection of Dexter and Laurel Streets — the site of the gun battle. But their views of how law enforcement handled the violence over 18 hours in April couldn’t be wider.

"They seemed very organized," Ryan said. "It seemed like they knew exactly what they were doing. The situation was, by nature, chaotic. I mean, these two criminals had come into the neighborhood to commit mayhem and murder and God knows what else. I had the impression that police forces were well coordinated."

"No, everyone was kind of on a different page," Doucette said. "I had to talk to so many different cops, because they weren't sharing information when it first happened, and as far as them being organized, as soon as the bombs started going off, they didn't know what the hell to do. They went running for cover and started shooting over their cars. It's not Afghanistan."

In the aftermath of the manhunt, Watertown Police have held community meetings with residents to hear their views, and to issue apologies to those whose lives were endangered.

"I promised the residents of Watertown that we'll do a real, serious look at ourselves and everything that happened here, to make sure what went right, what went wrong, and what we can learn from that," Deveau said. "It's going to take a while to do that, but we are in the process of working with the state."

But Watertown residents — even many of those who experienced close calls with bullets penetrating their homes — had mainly praise for law enforcement officials during the shootout and subsequent search for Dzhokhar Tsarnaev.

"I think that given the conditions, they were forced to do a job that they were not trained to do at all, and I don’t fault them for anything that happened," said resident Andy Fehlner. "I think we were just unfortunate to be so close to such a strange occurrence — I’m not sure why they seemed to randomly have chosen this very quiet street that we live on."

So why did the Tsarnaevs make their last stand in Watertown? We know they knew the town well. Tamerlan’s close friend lived here on Boylston Street, and the brothers had visited the neighborhood three times on April 18. The carjacking victim was forced to drive here earlier in the night. Now, Watertown police are investigating to see if there are deeper connections.

"We're still trying to flush that out," Deveau said. "We're part of a lot of detectives' meetings with the FBI and Boston, trying to retrace all the steps and everything, and that's an investigation that continues on. One of the things about Watertown is it's a very diverse community. Now we're trying to figure out if bad people can kind of just melt into there and not raise any concerns as they might in other areas of Massachusetts."

The Tsarnaevs also were familiar with Watertown’s roads —likened by one resident to the streets of Prague: circular, concentric and confusing. Outside Police forces got lost here.

That in itself is a lesson, says Deveau.

"In a true emergency, police vehicles got to have better GPS systems," he said. "Officers certainly weren't going to stop and program their address in, but we could've had more resources, quicker, if we had that type of technology."

Looking back, Peabody Police Chief Robert Champagne — who dispatched 12 officers 30 miles to assist in the search and arrest — says the massive police was not perfect, but …

"We learn lessons all the time," Champagne said. "This is a great opportunity to point out we did things a lot of things right, those days, and there's other things that we look at and talk about later, and say what could we do better the next time."

The police response in Watertown over an 18-hour period on April 19 included acts of heroism. But law enforcement’s response also posed an added public safety risk that serves as a cautionary tale in how to protect a community while dealing with terrorism in our midst.