Boston police commissioner Ed Davis, a now-familiar face in the wake of last month's bombings, testified this morning before the House Homeland Security Committee in Washington. He went off-script in the hearing, diverging from his expected call for more surveillance cameras  — maybe because it's unclear what good that would have done. Boston's existing cameras caught the Tsarnaevs, sure, but more cameras watching more targets would have done nothing better on prevention, little better on detection, and cost much, much more.

The hearing, meant to be the "first in a series" investigating the attacks, featured testimony from Massachusetts' undersecretary for public safety and security, a professor of risk analysis from USC, Commissioner Davis, and former senator Joe Lieberman. Lieberman testified first, presenting the case for increased focus on terror and apparently arguing incorrectly that Dzhokhar Tsarnaev's friends could have prevented the attacks.

When it was his turn, Davis first acknowledged the victims of the bombing and its aftermath. The commissioner then noted that working with citizens was important — more so than a reliance on technology. "There's no technical means [for identifying terrorists] that you can point to," he said. "There's no computer that can spit out the name. It's the community being involved in the conversation." 

This is a different position than what Davis had written to the committee in his prepared remarks. In those remarks, which are nonetheless part of the record of the hearing, Davis argued for stronger security around "soft targets" — like crowds gathered at marathons — and more security cameras. Noting that he didn't want to "move Boston and our nation into a police state mentality," Davis' remarks said that "images from cameras don't lie."

They can be viewed by a jury as evidence of what occurred.

These efforts are not intended to chill or stifle free speech, but rather to protect the integrity and freedom of that speech and to protect the rights of victims and suspects alike.

This is an argument that Davis has raised before. At the end of last month, he spoke with the Boston Herald, making largely the same case.

“We need to gather all the information we can as to what happened and make a determination as to the overall commitment the city of Boston has to the threat of terrorism,” Davis said. “That’s very, very important to me. It’s very important to the mayor. I’m sure there will be a lot of questions about that.” …

“Drones are a great idea. I don’t know that would be the first place I’d invest money, but certainly to cover an event like this, and have an eye in the sky that would be much cheaper to run than a helicopter is a really good idea,” he said.

The commissioner's prepared remarks did note that his department "had to rely almost exclusively on the support of our business partners to provide critical video surveillance along the finish line" — a less generous formulation of the relationship with the community than Davis spoke of during his testimony.

It was inevitable that an argument would be made, as we noted shortly after the attacks. But the flaws in the argument for more technology are as apparent as they were then.

As The Atlantic Cities noted in the aftermath of the attack, the city has an existing network of official cameras. A 2003 survey of Boston's downtown spotted a number of government and private cameras throughout the city center; in the intervening ten years, that number has certainly grown.

Davis gave those existing security cameras credit for their crucial role in helping to catch the Boston bombers. The images released by the FBI that triggered the Tsarnaev manhunt came from cameras on a restaurant along the marathon route — the Forum Restaurant, which Davis thanked in his testimony. Prior to that, the Boston Globe reported that one suspect — apparently Dzhokhar Tsarnaev — was recorded by a camera on a Lord & Taylor department store across the street from the second explosion (the scene at right). Even identifying those important snippets of film was heavily resource intensive. As The Atlantic's Alexis Madrigal pointed out last month, there doesn't exist software that can effectively sift through such video. So prior to release of the footage, "more than 100 analysts were painstakingly reviewing thousands of hours of surveillance and amateur videotape for anything suspicious," according to the Globe.

Some law enforcement agencies argue that a better strategy is to strengthen that informal network. Earlier this month, CBS spoke with officials from various agencies who made that point.

[I]n Houston, officials want to add to their 450 cameras through more public and private partnerships. The city already has access to hundreds of additional cameras that monitor the water system, the rail system, freeways and public spaces such as Reliant Stadium, officials said. ...

"If they have a camera that films an area we're interested in, then why put up a separate camera?" said Dennis Storemski, director of the mayor's office of public safety and homeland security. "And we allow them to use ours too."

(An engineer in downtown Los Angeles monitors the Department of Transportation's Automated Traffic Surveillance. Photograph by Reed Saxon/AP)

A deputy chief from Los Angeles argued about a camera network: "First, it's a deterrent and, second, it's evidence." That is a key point. While cameras can provide evidence to a jury, it is much less likely is that they can prevent such attacks. Deterrence might work for keeping people from committing vandalism; recent studies suggest that people behave differently when they know they're being observed. But for a terrorist intent on causing harm, it's not likely that would do much. Dzhokhar Tsarnaev, while clearly not a sophisticated criminal, didn't even bother to cover his face.

What's more, while there exists software that can identify suspicious packages, it's not clear how effective that detection mechanism is. More cameras necessarily require more staffing; even if software does the initial filtering, human law enforcement needs to be dispatched to investigate. That's expensive over the long term, in an effort to prevent very rare incidents — and still not fool-proof.

It's not clear why Davis decided not to focus on his prepared remarks today. It's possible that, knowing they were part of the record, he felt he could use his time to make a more emotional case. It's less likely that he did so because he recognizes that adding more cameras wouldn't have made much of a difference.