SANFORD, Fla. — Trayvon Martin’s DNA was not found on the grip of George Zimmerman’s gun, and Zimmerman’s DNA was not found under the unarmed teen’s fingernails, a law enforcement expert said Wednesday in testimony that prosecutors hope will refute the neighborhood watch volunteer’s self-defense claim.

Zimmerman has pleaded not guilty to second-degree murder and says he shot the 17-year-old in the chest to protect himself as Martin reached for his firearm during a fight.

Judge Debra Nelson dismissed jurors without the prosecution having rested its case as it had hoped to do by day’s end. Nelson won’t resume testimony until Friday morning, giving jurors the Fourth of July off. They will remain sequestered during the holiday break.

Florida Department of Law Enforcement DNA expert Anthony Gorgone also testified that Zimmerman’s DNA was found among blood on a shirt Martin was wearing under his hooded sweatshirt.

While cross-examining Gorgone, defense attorney Don West focused on the packaging of the DNA samples, suggesting it could have led to them being degraded. Gorgone told him that Martin’s two sweatshirts had been packaged in plastic while wet, instead of a paper bag where they can dry out, and when he opened the samples they smelled of ammonia and mold.

Florida Department of Law Enforcement analyst Amy Siewert also testified that tearing and residue on Martin’s clothing showed the gun was directly against him when it fired.

Prosecutors have sought to portray Zimmerman as a vigilante who profiled Martin as the teen walked home on a rainy night.

They called Gorgone on the same day they presented evidence that they say shows Zimmerman had aspirations of becoming a police officer and knew about Florida’s “stand-your-ground” law. The law says a person has no duty to retreat and can invoke self-defense in killing someone if it is necessary to prevent death or great bodily harm.