Defendant’s DNA May Have Been Transferred to Sweatshirt, Expert Suggests

By D.C. Witness Staff - October 26, 2022
Court | Daily Stories | Homicides | Shooting | Suspects | Victims |

In an Oct. 25 jury trial, experts in DNA and ballistics helped contextualize several key pieces of evidence in a 2017 homicide case.

On Aug. 10, 2017, Robert Moses, 23, and James Mayfield, 22, allegedly approached the intersection of Montana and Saratoga Avenues, NE while armed with .40 and .45 caliber handguns. Collectively, the defendants allegedly fired over ten rounds at people standing on Saratoga Avenue. One of the bullets struck 17-year-old Jamahri Sydnor in the head as she was driving, killing her. Three other bystanders were also struck and injured by stray bullets.

The prosecution called an expert in orthopedic medicine and surgery, and a practicing surgeon at George Washington University Hospital. He recalled treating a man who was injured during the Aug. 10 shootings. 

According to the expert, the man was already partly paralzed and rendered wheelchair-bound from having been previously shot in his back. When he heard gunshots near the Montana and Saratoga Avenue intersection, he promptly jumped out of his wheelchair. His leg then gave out, causing him to fracture his right hip and leg. The victim denied any loss of consciousness, neck pain, or head trauma but reported experiencing severe pain from these injuries.

Next, a DNA expert resumed his testimony from the previous day. The expert conducted a thorough review on the forensic reports conducted by a different expert, using computer software designed to analyze DNA. The software was specifically designed to disentangle complex DNA samples involving multiple potential people, and report how likely it was that each person’s DNA contributed to the sample.

According to the expert, when analyses were initially run on the sweatshirt, the software determined that Mayfield likely contributed to 8 percent of the DNA. It also found that a different individual accounted for 86 percent of the DNA on the sweatshirt’s interior.

The expert noted that Mayfield’s DNA matched the sweatshirt, as detected on the software. Still, he emphasized the inconclusive nature of the findings revealed by the software, claiming that he “can’t include or exclude [Mayfield] as a suspect.” 

The expert added that primary contributors to a DNA sample are generally very likely to have actually worn or repeatedly touched the sampled item, whereas minor contributions sometimes indicate the contributors’ DNA was transferred onto the item. As such, the expert noted that Mayfield’s DNA may have been transferred to the sweatshirt.

During their cross-examination, prosecutors referenced the expert’s DNA analysis in which he wrote, “the wearer of the sweatshirt is more likely the 86% contributor.” Although the statement presumes one single wearer, the expert clarified that others may have also worn the sweatshirt, though their DNA may have degraded over time. 

According to the expert, it’s possible that the DNA of the sweatshirt’s actual owner may have been washed off, leading them to only show up as the 8% contributor. He added that a different person may have worn the sweatshirt once while physically active and sweaty, and deposited enough DNA to show up as its primary wearer. 

Next, prosecutors called a forensic firearm and toolmark examiner to explain the types of “rifling marks” left on gun casings after bullets are fired, as well as what makes each mark distinctive.

The expert was shown several sets of photos of cartridge casings and bullet fragments, and asked to relay his previous analyses. According to the expert, each set of casings was covered in similar “random imperfections,” referring to the aftermarks and impressions left by the gun when fired. He also found that the first set of casings matched a .40 caliber firearm, while the second matched a .45 caliber firearm.

Moses, 23, was arrested on Aug. 10, 2017, while Mayfield, 22, was arrested on Dec. 28, 2017. They are charged with more than a dozen counts each, including first-degree murder while armed, assault with the intent to kill and possession of a firearm during a crime of violence.

DC Superior Court Judge Maribeth Raffinan set the trial to continue Oct. 26.