A police detective saw hair and blood spatter on the car driven by Thomas O'Brien (search), the Roman Catholic bishop of Phoenix who resigned after being charged in a fatal hit-and-run accident, according to court documents.

O'Brien told police he thought he had hit a dog or a cat or that someone had thrown a rock at his vehicle.

According to a search warrant affidavit released Thursday, a detective reported seeing hair and "biological material" in the shattered windshield and blood spatter on the roof of O'Brien's car. Police sought the warrant after approaching O'Brien on Monday about the hit-and-run accident and seeing the car in his garage, the affidavit said.

Police seized O'Brien's car. The affidavit said they also seized glass fragments from the driveway of O'Brien's home and black slacks and a black shirt.

O'Brien was charged Tuesday with a felony for allegedly leaving the scene of Saturday's accident, which killed Jim Reed, 43, who police said was jaywalking when he was hit by one car and then run over and dragged by another. Police haven't found the second car.

O'Brien's resignation Wednesday came two weeks after his public admission in an agreement with prosecutors that he sheltered alleged molester priests became public. Prosecutors say that deal spared him from prosecution on obstruction of justice charges.

The Arizona Republic reported Thursday that the Vatican demanded O'Brien's resignation. Reluctant to leave the post he held for 21 years, O'Brien finally was persuaded by a diocesan official to quit, the newspaper said.

A call to Pope John Paul II's (searchrepresentative to the United States, Archbishop Gabriel Montalvo (search), wasn't returned Thursday. Greg Leisse, an attorney for the diocese, said he wasn't in contact with anyone identified in the article as a participant in the discussion about O'Brien's resignation. Calls to other diocesan officials weren't returned.

Archbishop Michael Sheehan of Santa Fe, N.M., was named interim head of the Catholic Diocese of Phoenix until a new bishop is named. Sheehan said that could take as long as a year.

O'Brien, 67, faces continued legal scrutiny as authorities investigate whether alcohol, prescription drugs or other factors played a role in the accident.

He has declined to publicly discuss the accident.

If investigators find O'Brien was impaired from drinking alcohol, prosecutors could charge him with negligent homicide or manslaughter, Maricopa County Attorney Rick Romley said.

None of the evidence so far shows he was impaired, Romley said.

As it stands, O'Brien could be sentenced to anything from probation to nearly four years in prison if he is convicted of the current felony charge.