The crime scene was grisly. Three people, tied up with plastic zip ties, were shot execution style and set on fire inside a barn in a small town in rural Pennsylvania on a summer day two and a half years ago. One clung to life, but died the next day.

Now, the authorities say they have found the culprits behind the gangland-style killings.

In an indictment unsealed last week, 11 people who federal prosecutors said were members of the Black Guerrilla Family, a nationwide gang active in drug trafficking, murder and other crimes, were indicted in connection with the killings.

The authorities said the deaths began as part of a plot to silence a police informant that grew to include the killing of two others. The defendants have been charged with a range of crimes including murder, attempted murder, witness tampering, robbery, drug trafficking and illegal possession of a firearm by a felon.

One of the defendants, Jerell Adgebesan, was tied up one year after the killings by several other defendants who wanted to kill him because they suspected he was cooperating with law enforcement, according to the indictment. He has been charged with murder, witness tampering and drug trafficking.