As a Boston police manhunt took shape early this morning, Twitter feeds and Reddit threads were full of reporters and civilians tracking the events. Many people were using police scanners and apps that made Boston’s police frequencies accessible on the web. For those who knew where to tune in, these frequencies provided incredible drama. A shootout took place in real time. Those listening to the scanners were able to hear it all unfold.

That’s why scanners have been used for years by journalists and curious eavesdroppers: they put police actions in public. They allow any mildly savvy, curious person to listen in on the process of law enforcement as it happens. A 1997 article from the Society of Professional Journalists called police scanners “about as necessary in a newsroom as is the pen and notebook.”

A police scanner can be "about as necessary in a newsroom as is the pen and notebook"

But as police closed in on a second suspected terrorist on the run this morning, local police frequencies fell silent. The online feeds stopped. And a unified message went out: “Boston area law enforcement feeds are temporarily offline to protect law enforcement resources and their efforts during the manhunt underway in the Boston Metro area.”

You may have wondered, as many on The Verge’s staff did: why are police scanners public in the first place? Why aren’t they encrypted to keep any Joe Blow on the web from listening in?

According to John Banzhaf, there’s no legal reason why.

Banzhaf is a Professor of Public Interest Law at George Washington University who’s also a former scientist, engineer, and inventor.

He says there’s nothing wrong with police encrypting scanner frequencies. Furthermore, he says, “I don’t see any real problem with it.”

Some cities do encrypt police radio communications

Public access laws, such as the Federal Freedom of Information Act and its equivalent in most states, almost always allow police to withhold information while investigations unfold. The reason for this, at least ostensibly, is that disclosing information about ongoing cases could compromise what police are doing. People are investigated all the time without being charged, for example. If every lead in every case was made public, the possibilities for slander and libel would grow exponentially.

Along these lines, some cities do encrypt police radio communications so that they can't easily be intercepted by a run-of-the-mill scanner. Pasadena’s police, for example, have been encrypted for over a year.

There was some discussion — and a late 2011 public hearing — in Washington D.C. about its decision to have scanners go quiet. Police argued that criminals were using scanners to plan crimes and that public information officers had other means of informing people about whatever police events were occurring. Local media got upset, but, really, it’s up to police whether they allow scanners to be public or not. Scanners in Ft. Collins, Colorado went silent just this month.

So why don’t more cities encrypt their police scanners?

Banzhaf says it’s a matter of coordination when major events happen.

“There have been problems,” — in mass tragedies and other major crimes in big cities, he says — “where one police department had trouble talking with another police department, or a police department couldn’t talk to the fire department, or the fire department couldn’t talk with the people who could turn off the electricity.”

And this was without encryption.

“I believe in Murphy’s Law,” he says. “If something can go wrong, it will go wrong.”

The more open the communication system, in other words, the smaller the chance of problems during an emergency.

Encryption only exacerbates potential communication problems, in other words. When many departments need to speak with one another at the same time, there needs to be an easy way to do it. Public police scanner frequencies provide that. And most police bureaus in the United States have chosen to keep these frequencies open rather than deal with the hassle of organizing every agency into one encrypted frequency, Banzhaf says.

Encryption only exacerbates potential communication problems

But Gregg Leslie, legal defense director at Reporters Committee for Freedom of the Press, isn’t so sure.

Motorola’s LTE-based public safety network, he points out, was rolled out for the first time ever at last year’s Republican National Convention. As this system expands, it’s poised to eliminate the interoperability problems Banzhaf mentions.

Regardless, RCFP is against shutting the public out.

“In the end, our position is that [eliminating access to police scanner frequencies] harms public access,” Leslie says. “There’s a lot of public good done by letting the media and the public know what first responders are up to and it’s a shame that that could all go away.”