US law enforcement authorities are reportedly going after social media information of protesters at Donald Trump's presidential inauguration.

One unnamed individual, arrested at the protests in DC, received an email from Facebook's "Law Enforcement Response Team", which stated that Facebook had received "legal process from law enforcement seeking information about your Facebook account", according to a report by CityLab.

Civil liberties groups have slammed Washington DC police over the mass inauguration arrests, especially those of journalists and lawyers. The arrests reportedly saw police retaining the phones of those arrested, which the DC police continue to hold, raising concerns over potential pre-trial data mining.

The DC Metropolitan Police Department reportedly refrained from confirming whether they had asked Facebook to reveal information about users who were arrested. A spokesperson said: "MPD does not comment on investigative tactics."

On 27 January, the US Attorney's Office for the District of Columbia issued a subpoena, signed by a DC Metropolitan Police detective, asking Facebook for subscriber information of an unnamed inauguration attendee. Facebook also reportedly refrained from commenting on the matter.

However, according to Facebook's government request report database, US law enforcement agencies have sought information on the accounts of over 38,000 users between January and June 2016. In 80% of the cases, Facebook provided law enforcement with some kind of data.

The type of "legal process" law enforcement sends to Facebook for information on protesters matters, as it affects the amount and type of data that authorities can seize for information.

According to Facebook's legal guidelines, a search warrant could force Facebook to hand over content data, including "messages, photos, videos, timeline posts, and location information". In comparison, a subpoena or a court order would involve authorities getting their hands on less data. However, account holders' "name, length of service, credit card information, email address(es), and a recent login/logout IP address(es)" would still be made available to law enforcement.

Chicago-based police accountability group Lucy Parsons Labs director Freddy Martine suggested that information sought via a lower-level legal process could still be revealing. "Asking for IP data could point toward a physical location — i.e. an apartment — that people stayed in and could widen the net for further prosecution of other protesters," he said.

Donald Trump inauguration protestors’ hit with Facebook data searches from police – report
Facebook’s government request report database indicates US law enforcement agencies have requested information on the accounts of over 38,000 users between January and June 2016Reuters