Prince George's County State's Attorney Angela D. Alsobrooks was right to bring criminal charges this week against two county police officers accused of savagely beating University of Maryland student John McKenna last year, but it appears she hasn't yet gotten to the bottom of this case. There's reason to believe that many others beyond the two indicted officers may have been involved in the incident and its aftermath, and Ms. Alsobrooks, who took office in January, needs to bring all of those responsible to account if she is to convince the public that serious police misconduct will not be tolerated on her watch.

The incident occurred during a wild night of revelry after the Terps men's basketball team's March 2010 victory over Duke, which brought hundreds of rowdy celebrants onto the streets of College Park, where they set fire to trash bins and committed other acts of vandalism. There's no question authorities confronted a chaotic scene with the potential for serious damage to life and property, or that the post-game traditions at College Park have gotten way out of hand. Yet there's no evidence Mr. McKenna was in any way participating in the mayhem or indeed doing anything wrong at all when he was set upon by police in riot gear and repeatedly struck by truncheons and fists.

By chance, the assault was captured on video, and when the tape went viral on the Internet a few weeks later it showed a shockingly brutal, unprovoked attack that seriously undermined the credibility of the official version of what happened. Among other things, it suggested the two officers who have now been charged in the case, Reginald Baker and James J. Harrison, did not act alone but were part of a large group of officers on the scene who either abetted the attack, did nothing to stop it or actively tried to cover it up.

The video also appeared to contradict former county police chief Roberto L. Hylton's initial insistence that the problem was limited to a few bad apples and not related to any departmentwide pattern of abuse. At least three officers can be seen on the tape violently accosting Mr. McKenna, and a fourth officer wrote up charging documents against the victim and another student that turned out to be completely false. All this suggests the wrongdoing was not confined to just a few bad apples but that the system itself was rotten to the core.

It should be noted there's a big difference between obtaining the video record of a crime and being able to prove criminal charges against a defendant beyond a reasonable doubt. Camera images are often too blurry and indistinct to positively identify a suspect, and the lens only records events that take place within its limited field of view. What is happening outside the frame is often just as important as what's in it to understand the context of a situation.

But granted these limitations, it's hard to conclude from the evidence that the two officers now charged in the McKenna case were the only parties worthy of censure. How many others are implicated and how high up the chain of command the wrongdoing went are questions Ms. Alsobrooks needs to keep probing. At the same time, the current police chief, Mark A. Magaw, should be conducting his own review of the incident to find out how police training and supervision policies need to be changed in order to ensure such incidents aren't repeated.

By obtaining indictments against officers Baker and Harrison, Ms. Alsobrooks has taken an important first step toward providing justice for the victims of this crime. But she shouldn't stop there. The suspicion and mistrust of the police among county residents, who have long complained of officers abusing their authority, won't be assuaged until all those implicated in this shameful episode are called to account for their actions.