Martha Sosa, an American University law professor. “If there’s a problem as a result of an arrest, the police could make an arrest for assault if they had a legitimate reason for making an arrest [for that offense].”

A police officer can’t arrest someone solely because a 911 caller tells them they need someone, Sosa said. (Police officers don’t have the power to arrest someone for being drunk after the fact, she said.)

It’s up to the officer to determine why there is an arrest in the first place, said Lyle Clements, a constitutional law professor at the University of Missouri-St. Louis. And when an arrest is filed, Sosa said, that’s likely to lead to another complaint, further delaying a decision on whether the arrest was justified. “The police aren’t going to let the facts go as far as they want them to, so they’re going to make the arrests,” she said. “That’s always going to happen.”

In most circumstances, a 911 caller doesn’t need to disclose any other relevant information to obtain a police report, she said. But when a 911 caller wants police to have to take an extra step (because, say, they’re worried about their home being bombarded) or provide even more information (something like the location of a hostage, for example) police aren’t required to disclose those facts in the report, Sosa said. That’s an exception, but it’s a small one.

“Police know they do have to report the facts if they have a justification,” Sosa said. “They think it’s important to be proactive rather than reactive. And they’ve always suspected 911 calls for service are a legitimate concern.”

“When the fact that they can’t arrest you is in the 911 caller’s mind, you should go to the cops for an arrest,” Sosa added. “You can’t make an arrest without knowledge of the facts.”

The problem isn’t limited to callers who are making calls to report a domestic-violence situation, Clements said.

The Washington Post’s Fact Checker column on police responses to 911 calls has analyzed several years of FBI data to determine how often law enforcement agencies are responding to 911 calls and then reporting those calls for an alleged crime after they were filed. The Post found that over the past 12 months, “police responded to 1 in 3 911 calls related not to a crime but to