Defense attorneys Mark O'Mara (left) and Don West with George Zimmerman at the July 3 proceedings (pool/Getty Images)

(The Root) — The prosecution did not meet its goal of resting the case against George Zimmerman on Wednesday. That may be a good thing for the state because prosecutors arguably have not met their burden of proving that Zimmerman murdered Florida teen Trayvon Martin.

On the eighth day of testimony, the state presented the first DNA and blood evidence in the case in a continuing focus on discrediting Zimmerman's claim that he fatally shot the unarmed 17-year-old in self-defense.

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An expert testified that Trayvon's DNA was not found on Zimmerman's gun or holster, results the state are expected to use in closing argument to try to undermine Zimmerman's account that Trayvon grabbed the gun as they fought.

During the testimony by Anthony Gorgone, an analyst for the Florida Department of Law Enforcement, jurors for the first time saw the red, hooded sweatshirt Trayvon wore that night that has since become a symbol of public outcry over his death last year. As Gorgone explained his findings, prosecutors frequently held up the sweatshirt, encased in a clear glass frame, to show the bullet hole in the heart area surrounded by a large bloodstain.

Gorgone told jurors he did not find Zimmerman's DNA on the hooded sweatshirt or in scrapings of Trayvon's fingernails.

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The results are significant, given Zimmerman's version of the altercation. He says Trayvon punched him in the face, knocking him on his back, and then straddled him, punched him 25 to 30 times, cut off his breathing by placing his hands over his mouth and nose and repeatedly bashed his head against the sidewalk.

The prosecution is expected to argue that Trayvon couldn't have dealt out such a vicious, bloody beating without getting Zimmerman's DNA on his sweatshirt or fingernails.

"You did not find any of George Zimmerman's DNA on that?" Assistant State Prosecutor Bernie de la Rionda said.

"There was nothing that matched," Gorgone said.

For emphasis, Rionda asked again: "You also tested the hoodie's right sleeves and left sleeves, and you didn't find any of George Zimmerman's DNA on there, right?"

Judge Debra Nelson broke in before Gorgone replied, saying, "Asking and answered."

Gorgone did testify that he recovered Zimmerman's DNA from a single blood stain near the bottom of the sweatshirt Trayvon was wearing under the hoodie. DNA also came from a sleeve cuff, but he said the sample wasn't sufficient to be identified as Zimmerman's.

On cross-examination by the defense, Gorgone acknowledged that Trayvon's clothes were improperly stored in a plastic bag while still wet. He said it's possible that the packaging degraded the DNA evidence.

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Gorgone said he recovered some samples matching Trayvon's DNA from Zimmerman's clothes, but most of the DNA was Zimmerman's.

Zimmerman is charged with second-degree murder. If convicted, he could be sentenced to life in prison.

For much of the trial, the defense has neutralized many of the state's witnesses and raised clear doubts about the strength of the case against Zimmerman. The state's most effective testimony came on Tuesday, when the lead police investigator said Zimmerman's description of Trayvon as a "[expletive] punk" showed "ill will and spite" — a key element requirement for a conviction on second-degree murder under Florida law.

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In other testimony on Wednesday, firearms expert Amy Siewert said the gunpowder burns on Trayvon's hoodie were consistent "with a contact shot." She clarified that her finding meant the gun muzzle was "touching" Trayvon's clothes when the weapon fired — not "pressing," as the prosecution argued in its opening statement.

Jurors also heard testimony from two of Zimmerman's former professors at Seminole State College, who said he was a student in their courses on criminal law and investigations. One of them, attorney Alexis Carter Jr., extensively covered Florida's self-defense laws, including "Stand your ground."

"He was probably one of the better students in the class," Carter said of Zimmerman. Carter added that Zimmerman earned an A in the course.

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The state says Zimmerman's coursework proves he knows more about criminal law than he claims. Zimmerman said in an interview with Fox News last year that he hadn't known about the "Stand your ground" law before the shooting.

Carter said Zimmerman was his student in 2010, nearly two years before the shooting.

The state contends that Zimmerman's course work illustrates his knowledge of criminal procedure and policing techniques, potentially enough to help him craft a false self-defense claim.

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Carter, under cross-examination by the defense, explained in detail the Florida's self-defense statute that he taught Zimmerman and other students.

He said he taught that self-defense is lawful "when you have a reasonable apprehension of death or grievous bodily harm. But when stuff hits the fan, you're judged by jurors. Your actions have to meet a reasonable standard objectively, so whether or not a reasonable person in your position would have felt the same way."

Carter said he also discussed an "imperfect defense," in which a person "takes it too far" by acting "unreasonably in countering the forces that was presented to them."

In court Friday:

The state is expected to conclude its case, but not before calling a few highly anticipated witnesses, such as the medical examiner who performed the autopsy of Trayvon's body. That testimony likely will address the trajectory of the bullet and distance it traveled before entering Trayvon's chest — key details that could reveal more about the fight.

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In addition, Trayvon Martin's mother, Sybrina Fulton, and brother could take the stand. Fulton is expected to say that she believes the voice heard screaming for help on a 911 was her son's. An FBI expert testified about the agency's inability to identify the voice. 

Corey Dade, an award-winning journalist based in Washington, D.C., is a former national correspondent at NPR and political reporter at the Wall Street Journal, the Boston Globe and other news organizations. Follow him on Twitter.

Corey Dade, an award-winning journalist based in Washington, D.C., is a former national correspondent at NPR and political reporter at the Wall Street Journal, the Boston Globe and other news organizations. Follow him on Twitter.