An expert witness at Robert Blake's (search) murder trial said Tuesday he could not be sure whether possible gunshot residue on the actor's hands and clothes came from firing a gun the night his wife was shot to death.

Deputy District Attorney Shellie Samuels asked coroner's criminalist Steven Dowell: "Is there anything about your tests that would exclude the possibility that the defendant fired a gun that night."

"No," Dowell said.

On cross-examination by the defense attorney M. Gerald Schwartzbach, Dowell acknowledged that the residue particles found on Blake's hands and clothes the night Bonny Lee Bakley (search) was killed could have come from the revolver he carried, his gun collection at home or other sources, even police officers.

The prosecutor suggested in her questioning that the actor purposely ran his hands through his hair, held glasses of water, rubbed his hands on grass at the scene and engaged in other activities that could have removed the particles before police conducted tests.

Dowell could not say whether those activities could have removed all gunshot residue.

Bakley, 44, was shot in the couple's car on the night of May 4, 2001. Blake, the former star of "Baretta (search)," claims he found her fatally wounded after leaving her briefly to return to a restaurant to retrieve a handgun he carried for protection and inadvertently left behind. That gun was not the one used to kill Bakley.

Dowell acknowledged that Blake's clothing at one point was stored in a box that a detective brought from a police station squad room, and that officers often come into the station from the firing range.

"The squad room is a place you would expect to find gunshot residue?" asked Schwartzbach.

"That's fair, yes," said Dowell.

Dowell testified that Blake's clothing was collected at his home, where he kept a gun collection, and that gunshot residue could also have rubbed into the clothing if Blake leaned into the car in which Bakley was shot.