Samuel Stewart a DNA analyst from the South Carolina Law Enforcement Division speaks during the murder trial of former North Charleston Police Officer Michael Slager, Thursday, Nov. 10, 2016, in Charleston, S.C. Slager is on trial facing a murder charge in the shooting death of Walter Scott, who was gunned down after he fled from a traffic stop. Ninth Circuit Solicitor Scarlett Wilson is seen at left. (Grace Beahm/Post and Courier via AP, Pool)

Samuel Stewart a DNA analyst from the South Carolina Law Enforcement Division speaks during the murder trial of former North Charleston Police Officer Michael Slager, Thursday, Nov. 10, 2016, in Charleston, S.C. Slager is on trial facing a murder charge in the shooting death of Walter Scott, who was gunned down after he fled from a traffic stop. Ninth Circuit Solicitor Scarlett Wilson is seen at left. (Grace Beahm/Post and Courier via AP, Pool)

CHARLESTON, S.C. (AP) — A fired white police officer’s defense lawyer told jurors at the start of his murder trial that he was provoked to shoot an unarmed fleeing black motorist, when the man “physically and forcefully resisted” being subdued by a stun gun “to the extent that they were both fighting on the ground.”

A DNA expert’s testimony Thursday cast some doubt on that argument, revealing that none of the North Charleston officer’s genetic material was found under the dead man’s fingernails, and that a DNA analysis of his Taser was inconclusive.

Samuel Stewart of the South Carolina Law Enforcement Division testified at the trial of Michael Slager, whose shooting of 50-year-old Walter Scott in April 2015 was captured on a bystander’s cellphone and shared worldwide.

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DNA from the Taser “is a mixture of two individuals, and Walter Scott and Michael Slager can’t be excluded as contributors to the mix,” Stewart testified. He also said DNA from three other places on the stun gun did not belong to either Scott or Slager.

Stewart said blood stains on Slager’s uniform shirt and pants also were analyzed. He testified that the blood matched Slager’s own DNA, and that while there was another person’s DNA, there was not enough of it to analyze its source.

Scott tried to flee after the 1990 Mercedes Benz he was buying from a friend was pulled for a broken taillight. His brother, Anthony Scott, testified that he told he told his brother a few days before the shooting that he was concerned about the purchase.

“I told him I didn’t think it was a good idea and he needed to reconsider buying that car, because he lived in North Charleston,” Anthony Scott said, adding that city police were known to profile black motorists.

He also worried that his brother was buying the car even though he was behind on child support. Family members have said that Walter Scott may have tried to run to avoid being jailed for non-support.

Court adjourned for the week on Thursday with the prosecution, which has already called 27 witnesses, still presenting its case. There is no court Friday because of Veterans Day.

Lt. Tracy Thrower, a ballistics expert with SLED, also testified Thursday, confirming that the bullets in Scott’s body were fired by Slager’s service revolver.

The week’s final witness was Lt. Charles Ghent of the South Carolina Law Enforcement Division, who described interviewing Slager after the shooting.

Slager described being afraid for his life, and said he shot Scott after the motorist got control of his stun gun and pointed it at him. Ghent said he was one of the SLED officers who later arrested Slager after showing him the cellphone video.

Slager faces 30 years to life in prison if convicted of murder.