Walker attempted to raise the issue through all of the DNA expert testimony yesterday, which lasted several hours and included four witnesses. At one point Santos and Walker engaged in a mini-debate over how to describe the contamination, with Walker calling it a "dramatic mistake" and a "serious problem" and Santos responding that it was "not dramatic" and "not a 'serious' problem."
The state's case against Grimes does not rely entirely on DNA evidence. The jury has already heard testimony from two witnesses who place Grimes at the scene of the crime and the pistol in his hand during the 12 hours before the shooting.
Grimes is charged in the fatal shooting of Detective Troy Lamont Chesley Sr., 34, as Chesley tried to unlock the front door of his Forest Park apartment in the 4500 block of Fairfax Road after getting off a late shift in January 2007. Police said Chesley returned fire, wounding Grimes in the leg.
Sgt. Richard Purtell yesterday testified that Grimes left a trail of blood as he limped from the crime scene and around the block to Westchester Road, where the trail stopped. Police believe Grimes fled the scene in a green Dodge Caravan, driven by his then-girlfriend, Kelly Carter.
Purtell said police called in a bloodhound to trace the trail. The pistol was found halfway through it, according to charging documents.
Yesterday lab employee Jocelyn Carlson testified that DNA collected from blood stains on two leaves and a rock along the blood trail all came from Grimes, as did a blood sample taken from the Westchester Road sidewalk in Northwest Baltimore.
Those samples were not contaminated. In all, at least 12 untainted DNA samples were described to the jury yesterday.
But the weapon police say Grimes used - equipped with a laser-targeting device and a special grip - was not handled as carefully.
Santos said yesterday that technician Victor Meinhardt, who worked in the lab's mobile unit that travels to crime scenes, left his DNA on the grip of the pistol as he dusted it for fingerprints.
The source of other DNA found on the grip could not be determined. DNA experts testified they could rule out Meinhardt, Carter or another passenger in the van, Joshua Morris, as the source, but they couldn't be sure it was Grimes.
As for the contamination, Meinhardt testified: "There's a thousand ways it could have happened. I could have coughed, sneezed or scratched my head."
Sterling Clifford, a spokesman for the police department, played down the importance of analyzing partial DNA profiles, like the one found on the pistol grip. Partial DNA profiles, much like partial fingerprints, "are limited in their usefulness," he said.
Santos and Sharon R. Holback, chief of the state's attorney's office's forensics division, have told public defenders that they believe the DNA contamination occurred at crime scenes throughout the city rather than inside the laboratory at police headquarters, according to Baltimore Public Defender Elizabeth Julian.
Julian has asked to review all case files involving contaminated DNA. Santos and Holback promised to meet with her again to go over the issues in three weeks.
Baltimore Sun reporter Julie Bykowicz contributed to this article.
