You'd think he'd done this before

Lynn Olanoff has an article in the Lehigh Valley Express Times about another 'expert' witness:

It was almost O.J. Simpson and the gloves all over again Friday in the Mary Jane Fonder murder trial.
As state police ballistics expert Mark Garrett demonstrated how to load bullets in the suspected murder weapon -- Fonder's .38-caliber Rossi revolver -- the cylinder wouldn't close. During Simpson's murder trial, he could not fit his hands into gloves considered a key piece of evidence. Garrett blamed the cylinder's malfunction on possible rust. A minute or two later, he got it to close.
Fonder's defense attorney Michael Applebaum pointed out the gun's failure in his cross-examination. "If you can't close this, you can't fire the weapon?" he asked.
"Correct," Garrett confirmed.
Fonder, 66, of Springfield Township, Bucks County, is charged with first-degree murder in the Jan. 23 death of Rhonda Smith, 42, of Hellertown. Authorities allege Fonder killed Smith at Trinity Evangelical Lutheran Church in Springfield Township because Fonder was jealous of the attention Smith received from church members.
Garrett was called as a prosecution witness because he tested all the ballistic evidence involved in the case. Fonder's gun fired the bullet found in Smith's head along with another bullet piece found alongside her body, he said. Every gun barrel is unique and leaves different imprints on bullets, Garrett said. The two bullet pieces had the same pattern, he said.
Applebaum asked Garrett if it were possible the gun's barrel or serial number were replaced. Garrett said he didn't know about the barrel, but a replaced serial number is usually much smoother than the original. Fonder's gun's serial number still has grooves, he said.
Prosecution witness Elana Foster testified gunshot residue was found in three places within Fonder's car. Gunshot residue was found on the car's driver's seat, the turn signal knob and the driver's door armrest, she said.
Applebaum continued a theory he started Thursday that police could have unintentionally transferred the residue from their uniforms to the car when they searched it. He asked Foster if she had read studies naming police stations as the one of the most prolific places to find gunshot residue. She said she was familiar with some tests showing residue in the backseat of police cars. "Gunshot residue can be transferred," Foster said. "We can say the particles are present but how they got there, when and from whom we can't say."

Rico says no, it wouldn't close because it'd been fired and not cleaned; the powder residue attracts moisture, swells, and jams the mechanism. (Rico has had this happen when he got lazy and didn't clean his gubs.) You can also match powder residue to powder found in the remaining shells; it's not a perfect scientific match, but you can at least exclude things like residue from cops' clothing as being from some other batch. This is not only bad witnessing, it's bad lawyering; clowns, the lot of 'em...