Why Baltimore's star prosecutor will have a hard time convicting the 6 charged cops

Baltimore state's attorney Marilyn Mosby filed charges against six members of the city's police department Friday in connection with the death of Freddie Gray, a case that experts say is both rare and difficult to prove.

"I can't think of any situation like this where six officers get indicted where there's these kinds of charges in one setting," Bowling Green State University professor Philip Stinson told The Baltimore Sun.

Stinson said this fits into a trend of videos playing a role in controversial police cases across the US. Before the charges against the officers were brought, video circulated of Gray being dragged limp into a police van, which may have led to his death.

After placing Gray in the van, officers reportedly stopped at least four other times but never properly secured him with a seat belt, Mosby said at the press conference, The Baltimore Sun reports. They also allegedly failed to give him medical attention, though he asked for it twice, according to Reuters.

However, as The New York Times points out, "much of what happened to [Gray] occurred either in the presence of the officers who have been charged or while he was alone in the back of the police wagon."

It's unlikely that police officers would turn on each other during a trial, due to the loyalty that typically runs through departments, David A. Harris, a University of Pittsburgh law professor and an expert on racial profiling, told The New York Times.

Jurors are often "inclined to give [police officers] the benefit of the doubt," according to The Times, because behavior "such as beating or even shooting another person" is assumed to be part of a cop's job.

"It's always difficult to get a guilty verdict against a police officer except in the worst and strongest cases," Harris told The Times. "A police officer comes into a courtroom not just presumed to be innocent, but presumed to be the good guy."