Following the news that Dallas shooter Micah Johnson bought a semi-automatic rifle from a private seller he met on Facebook, Massachusetts Sen. Ed Markey sent a letter to the social media network what steps it has taken and plans to take to restrict gun sales from being arranged on the service.

Johnson purchased the gun in 2014, when Facebook didn’t have the same rules prohibiting gun sales that it does now. And the gun Johnson purchased was similar to the one he used in the shooting but reportedly not the same, and it was bought legally under Texas law. But Markey wrote that he was also concerned about how it easy it is to find posts about gun sales and wanted to know how Facebook (and Instagram, which Facebook owns) planned to address this.

As Forbes reported, Facebook hasn’t been proactive about preventing gun sales postings by individuals or groups devoted to selling guns the way sites such as eBay are or the way it monitors its own users for child pornography posts. Instead, it relies on users to report violations—with somewhat mixed results, according to people who have attempted to report gun sellers and groups to the social media giant. The most prominent of them, Mike Monteiro, has been temporarily banned from Facebook several times for his posts about successful gun reports that Facebook claimed violated “community standards.”

“I remain deeply concerned that gun sales on Facebook and Instagram—or sales posted online but negotiated and concluded offline—may circumvent or violate state and federal laws,” Markey wrote.

The senator is asking Facebook to answer questions regarding its enforcement efforts in the past and future, list the law enforcement agencies that have requested its assistance on gun sale investigations and the results of those requests, and give any information about Johnson’s attempts to purchase that AK-47 through the service. He has asked the company to respond by July 27, but there is nothing requiring Facebook to do so.

A spokesperson for Facebook and Instagram told Vocativ, “We prohibit people from using Facebook and Instagram to offer and coordinate private sales of firearms. Any content that violates this policy will be removed as soon as we become aware of it—whether it is in groups, on accounts, or on pages.”