(CNN) -- A prisoner killed in a Maryland county jail on Sunday was a victim of "vigilante justice," Prince George's County Chief Executive Jack Johnson said.
Ronnie White, 19, died of strangulation and asphyxiation and had two broken bones in his neck, an autopsy showed.
An attorney for White's family said that because White was being held in solitary confinement at the Prince George's County Correctional Center, a corrections officer would have had to let whoever killed the prisoner into his cell.
His death came two days after his arrest in connection with the death of Prince George's County police Cpl. Richard Findley, who died Friday after being struck by a truck. Authorities believe that White was driving the truck, which was thought to be stolen. Police were attempting to flag it down when Findley was struck.
"The killing of the officer is absolutely abhorrent, but also, Mr. White was presumed innocent and deserved his day in court just like any other citizens," Johnson said Monday night. "We live in a constitutional democracy, and no one has the right to be judge and jury."
The FBI's Baltimore field office said it has opened a civil rights investigation into White's death. The Justice Department said Tuesday that federal prosecutors have been in contact with the state police and FBI as well as county prosecutors and the department's own Civil Rights Division.
"In support of the Prince George's County State's Attorney's Office, which intends to retain lead responsibility for the criminal investigation, the U.S. Attorney's Office will provide guidance and legal advice to the officials looking into the death and seeking to develop evidence of criminal violations," the department said in a written statement.
Johnson said Monday that he had requested that the Maryland State Police conduct an independent investigation into White's death.
White family attorney Bobby Henry said there are only two ways someone could get into solitary confinement. Watch why death has outraged family »
"You either have to be buzzed in from the booth -- I believe it's called the control booth -- you need a key from there, or you have to get a key from one of two officers who were assigned to his unit on that day," Henry said.
The attorney said a "yet to be identified person or persons took it upon themselves to be the judge, jury and executioner for Mr. White."
"The family of Ronnie White is absolutely, unequivocally outraged, incensed and deeply saddened that the life of their loved one could be taken so cold[ly], so callously," Henry said Tuesday. "Something is dreadfully wrong with the system."
County authorities have said that police are not suspects and that seven corrections officials and an unspecified number of supervisors were the only ones authorized to be in White's cell. None has been suspended or removed.
There were no surveillance cameras in the area of the jail where White was being held. White had not had the opportunity to meet with an attorney, Henry said.
A physical conducted when White was processed revealed no health issues, according to Johnson. He was checked regularly in his cell and appeared fine when corrections officers saw him at 10:15 a.m. Sunday. When officers brought him lunch 20 minutes later, he was unconscious and without a pulse, Johnson said.
Henry said White's family was not notified of his death until several hours after it occurred. They were told to go to Prince George's Hospital to identify the body, he said, but upon arrival were told the state medical examiner's office had taken custody of the body and it had been taken to Baltimore.
"At this very moment, the family has not even seen the body of their loved one," Henry said. "They have been denied the opportunity to start the grieving process which naturally must occur."
He said White's family is calling upon the Department of Justice, the FBI, the Maryland State Police and county officials "to conduct a thorough and exhaustive investigation into all of these tragic events, beginning with the events of Friday, June 27, and continuing up until this time."
Prince George's County State's Attorney Glenn Ivey said a grand jury will be convened in the case. He said his office, which will handle any prosecutions that might result, is keeping an open mind. "We'll follow the evidence wherever it leads," he said.
He added that he's "never seen one like this. We've had deaths in custody, but this could be a unique one."
CNN's Jeanne Meserve and Mike Ahlers contributed to this report.