Officials are investigating seven correctional officers who had access to an inmate found strangled Sunday in a Prince George's County, Md., jail where he was being held alone in a maximum security cell.

Ronnie White, 19, was arrested Saturday and charged with running down and killing Cpl. Richard S. Findley, a Prince George's County police officer. The Maryland medical examiner ruled Monday that White died from strangulation. Two small bones in his neck were broken.

On Tuesday, the FBI and Maryland State Police turned their investigation to guards at the Upper Marlboro, Md., jail, which has a history of security lapses. County State's Attorney Glenn Ivey said his office would convene a grand jury to review evidence in the case. He said investigators were scrutinizing seven correctional officers who had access to White, who was being held separately from other inmates. Ivey also said other workers at the county jail and inmates would be questioned.

"We'll follow the evidence wherever it leads," he said.

White had been charged with first-degree murder in Findley's death. The officer had been leading an investigation into a car theft ring when he pulled over a motorist in rural Maryland. As he was climbing out of his police cruiser, he was struck by a pickup. Police said they believed the truck was stolen and that White was the man at the wheel.

They arrested White and three other men hours later at a nearby apartment complex where the pickup was parked. Findley had been rushed to a nearby hospital. He died a short time later from complications related to massive head trauma.

White's death is the latest in a series of security lapses at the jail, which is 20 miles outside Washington in one of Maryland's largest counties. Last month, the county's corrections director was fired after guns vanished from the armory. In February, a former police official convicted of second-degree murder was found with a handcuffs key.

A corrections officer suspected of being a gang member was charged in March with bringing cell phones to inmates who were members of the Bloods street gang. And earlier this year, two female officers were suspended for allegedly having sexual contact with inmates.

More than 450 guards work at the 20-year-old facility, which had an average daily population of 1,489 prisoners during the 2007 fiscal year. White was being held in a cell by himself, to protect him from other prisoners, because of the high profile of the case.

"This shouldn't happen," County Executive Jack Johnson said Monday night. "Every citizen we bring into our custody should be protected."

Curtis Knowles, head of the county's correctional officers union, said Tuesday that union lawyers advised him not to comment on the case because of the investigation. On Monday, he urged people not to reach any conclusions before the investigation had run its course.

Corrections officials have said White had no visible signs of trauma on his body when guards bringing him a meal found him slumped on the floor next to his bed about 10:30 a.m. Sunday. He had been checked 15 minutes earlier and had 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.

None of the seven guards or the unspecified number of supervisors who could have had contact with White have been suspended or placed on leave, according to Vicki Duncan, spokeswoman for the corrections division.

White had a prior criminal record that included serving time for drug charges.

Members of his family did not attend a news conference Tuesday held by their attorney, Bobby G. Henry Jr., and they could not be immediately reached.

"This did not happen on some dark, abandoned, lonely road," Henry said. "This happened in broad daylight, in the custody of county officials. Everyone who has someone or knows someone who is in the county correctional facility should have a problem with that."

Findley, 39, was a 10-year veteran of the county police force. A funeral is scheduled for Thursday, and Maryland Gov. Martin O'Malley ordered state flags to be flown at half-staff until then.

Compiled from NPR and Associated Press reports.