The case, from an M&T Bank robbery in 2006, was one of several real-life examples that Kercheval discussed Thursday during a presentation at the Washington County Free Library in Hagerstown.
Kercheval, who works with two other forensics investigators at the Western Maryland Regional Crime Lab, said the case illustrated the importance of backing up eyewitness accounts with physical evidence.
"People don't intend to mislead us," Kercheval said. "They just make observations that aren't correct."
About 30 people gathered in the library's downstairs meeting room for the presentation, which also covered investigations of a break-in into four military tanks, a man found beaten to death outside the McDonald's on Dual Highway and a body found in the woods outside Funkstown.
Some participants, such as 12-year-old Nathaniel Laye of Smithsburg, said they were interested in forensic investigation because of the TV show "CSI."
"I thought it was going to be like the show," said Nathaniel, who wants to be an forensic investigator when he grows up.
But Kercheval made it clear there are many differences between television and reality.
"They drive around in Hummers," he said. "I drive around in a 1997 Chevy Astro van."
About 90 percent of the Hagerstown forensic team's time is spent on paperwork and reports, which are essential memory aids when cases finally go to trial five or 10 years after the incident, Kercheval said.
A large bulk of time is spent processing drug evidence -- about 1,000 cases a year, he said. But investigators also get their share of robberies, homicides and violent crime.
"Every day's exciting," said Kercheval, who is on call 24 hours a day, seven days a week, 365 days a year. "You kind of feel like a pinball bouncing in a pinball machine."