Police in Washington, D.C. want Facebook to hand over data on protesters.

The D.C. police department subpoenaed Facebook for information regarding several protesters arrested while demonstrating against the inauguration of President Donald Trump on Jan. 20.

A document obtained on Monday by CityLab shows the U.S. Attorney’s Office for the District of Columbia issued a subpoena to Facebook on Jan. 27, which was signed by an officer at the police department. The document appears to show D.C. police are looking for the social data of several protesters.

UPDATE: US Dist Attorney of DC & DC police subpoenaed Facebook for account data on numerous inauguration protestershttps://t.co/kpCPEwxLde pic.twitter.com/Nei9RKH089 — George Joseph (@georgejoseph94) February 6, 2017

Police arrested more than 200 people during the inauguration protests, including journalists. Defense attorney Benjamin Carraway almost immediately filed a class-action lawsuit against D.C. and park police, alleging officers had corralled peaceful demonstrators and used chemicals in attempts to control them.

D.C. police said no one at the department could comment on the subpoena given the lawsuit. A Facebook representative said the company doesn't "comment on individual requests," though the company's law enforcement guidelines might offer a glimpse of what's ahead.

"A valid subpoena issued in connection with an official criminal investigation is required to compel the disclosure of basic subscriber records," the guideline reads. Those records "may include: name, length of service, credit card information, email address(es), and a recent login/logout IP address(es), if available."

Issuing a subpoena is a more direct way for police to try to get the social data of people they have their eye on, but law enforcement departments are often trying to obtain social data from protesters in one way or another. Officers ask Facebook to tap into messages sent on the social network as well as messages sent on WhatsApp, which Facebook owns. They have also used social media monitoring services such as Geofeedia, Media Sonar, Digital Stakeout and others to track the social accounts of protesters in real time.

This time, though, police swept up protesters in mass arrests and kept their phones. Many arrestees were charged with felony rioting, and police have reportedly mined their phones for whatever evidence they might obtain. What they can't get with a phone in their hand, they'll try to get from Facebook.