The top prosecutor in St. Louis has accused the city’s Police Department of obstructing the investigation into the killing of an officer whose death last week was originally described as an accident that happened while she was playing Russian roulette with a colleague.

Officer Katlyn Alix was shot in the chest and killed last Thursday by Officer Nathaniel R. Hendren in his home, the police said. Officer Hendren, who was on duty when he shot Officer Alix, was charged last Friday with involuntary manslaughter. Officer Alix, whose funeral was held Wednesday, was off duty at the time of the shooting.

But the investigation into her death has not gone smoothly, according to Kimberly M. Gardner, the St. Louis circuit attorney.

In a letter on Monday to John Hayden, the St. Louis Metropolitan Police Department commissioner, and Jimmie Edwards, the public safety director, Ms. Gardner raised concerns with the investigation that included the gathering of evidence and what she said was the Police Department’s rush to label the shooting an accident.