UPPER MARLBORO, Md. -- A man arrested in the hit-and-run death of a police officer was found strangled in his cell, and investigators focused yesterday on guards at the suburban Maryland jail.

State police took over the investigation of the death of inmate Ronnie L. White, which shocked and angered officials in Prince George's County. County Executive Jack Johnson likened it to "vigilante justice."

But Johnson moved to curb speculation that White's death was the result of police officers seeking revenge. He said the slaying was "unrelated to any act" by police.

White, 19, was arrested Saturday on charges of ramming a stolen pickup truck into police Cpl. Richard Findley on Friday.

Corrections officials have said White had no visible signs of trauma on his body when guards bringing him a meal found him on the floor Sunday about 10:30 a.m. He had been checked 15 minutes earlier and appeared to be well. A preliminary autopsy by the state medical examiner in Baltimore ruled the death a homicide and found two broken bones in his neck.

Seven guards and an unspecified number of supervisors could have had contact with White, who was being held separately from other inmates. None have been suspended or placed on leave during the investigation, said Vicki Duncan, spokeswoman for the corrections division.

County State's Attorney Glenn Ivey said his office would convene a grand jury to review evidence in the case.