More people may be arrested in connection with violent Inauguration Day protests as authorities sort through evidence of the rioting that left six police officers injured and caused tens of thousands of dollars of damage to vehicles and store windows, a D.C. prosecutor said.

During the Jan. 20 inauguration of President Trump, 230 people — many of whom defense attorneys said are college students who live outside of the District, Maryland or Virginia — were detained in a mass arrest and charged with felony rioting. Since then, authorities have been working through the cases in an effort to identify each person’s role, then pursuing some cases and dismissing others.

As of Friday, prosecutors had dropped charges against nine people. Four of those are journalists who were swept up as they reported on the protests. Prosecutors would not say why they dropped the cases against the other five.

Court records show that 63 of those arrested have so far been indicted on a charge of felony rioting, which carries a maximum of 10 years in prison and a fine of up to $25,000. The remaining cases are making their way through the court system.

In D.C. Superior Court last week, one of the lead prosecutors told a judge additional arrests, as well as dismissals, could occur in coming days.

A large crowd cheer as their friends are released from the D.C. Superior Court on Jan. 21. (Marvin Joseph/The Washington Post)

“We are continuing to get new information every day. In the next week or two, we expect to bring in more defendants,” Assistant U.S. Attorney Jennifer Kerkhoff told Judge Danya Dayson during the Thursday hearing.

Investigators within the office are working to view still photos and hundreds of hours of video to pinpoint the actions of people involved in the rioting. Undercover D.C. police officers were dispatched at the protests with cameras, according to a court charging document. And D.C. officers wore body cameras during their interactions with protesters.

Several videos have been circulated publicly, some of which have been posted on YouTube.

Still, identifying particular people may be a challenge, as many had their faces covered with goggles, hats and black scarves.

In addition, defense attorney Jason Flores-Williams said three of his clients received emails from Facebook alerting them that prosecutors have subpoenaed information from their accounts. Flores-Williams said he plans to seek a court injunction blocking Facebook from releasing the information.

The attorney said he believes prosecutors wanted to look at the postings and friends of his clients.

“This violates their rights. And what does that have to do with the case? It’s broad and overreaching. They’re just trying to intimidate people and scare them,” Flores-Williams said.

A spokesman with the U.S. attorney’s office declined to comment on the Facebook request allegations, or generally on the cases.

A Facebook spokesman confirmed Friday such emails have been sent to users regarding subpoenas involving the Inauguration protests, but the spokesman declined to comment further.

At last week’s hearing for 10 of those indicted, one defense attorney showed some signs of his strategy in the case.

Matthew Davies, with the District’s Public Defender Service, argued that the U.S. attorney’s office should recuse itself from prosecuting the case, because the president selects and nominates the U.S. attorney. Defense attorneys have argued that a special prosecutor or even prosecutors within the District’s Office of the Attorney General should be appointed. The judge said she would respond to the attorney’s petition at a later date.

Davies represents 22-year-old Breton Strasburger of Pittsburgh, who is charged with rioting. He also argued that prosecutors had failed to specify what his client — or any of the defendants — were alleged to be doing at the time of their arrests.

In charging documents, authorities recount the actions of the group but do not elaborate on any individual’s alleged role.

Some defense attorneys for the protesters have argued that prosecutors are rushing to indict the defendants to avoid preliminary hearings, where the prosecutor would have to present evidence of the allegations.

“Without such specifics or merit, a judge could find there is no probable cause and order the case dismissed,” said Betty ­Ballester, head of the court’s Trial Lawyers Association, who is not involved in the case. “They don’t want to have to prove their case early on.”

D.C. authorities had prepared for the possibility of mass arrests. In anticipation of the large number of protests on Inauguration Day, prosecutors met with police officials and attorneys within the D.C. police department to discuss strategies.

The cases have been assigned to the U.S. attorney’s office major crimes unit, a division that includes veteran homicide prosecutors such as Kerkhoff.

The incidents occurred in a four-block area between the intersections of 13th and O streets NW and 12th and L streets NW.

Other cases have shown the challenges of prosecuting those picked up in mass arrests. Last November in Portland, Ore., 120 people who were part of an anti-Trump demonstration were detained. Two months later, prosecutors were forced to drop the cases of about 80 of them. The cases were basically dropped because police were unable to identify each person arrested as being involved in criminal activity by viewing video taken during the arrests.

Reviewing hundreds of hours of video footage, said Kirsten Snowden, chief deputy district attorney for Portland, was not an option.

“It was painstaking and very time consuming,” she said. Since most of the cases dropped were misdemeanors, Snowden said her office was then allowed to focus on the more serious felony offenses, such as vandalism. Unlike in Washington, only two people arrested in Portland were charged with rioting.