The Marshals had put out a call for help from the public in the manhunt for Ruffo, who was convicted of a $350 million bank-fraud scheme in the 1990s and is one of the federal agency's most wanted fugitives.
A fan seen on TV behind home plate at a Dodgers-Red Sox game in 2016 bore a strong resemblance to Ruffo - so much so that a relative of the fugitive called in the original tip.
The Marshals tried to track down the original ticketholder, but the ticket had been resold more than once and the final purchaser and seatholder could not be identified.
After a story about the case aired on ABC and other media outlets this week, a person from the Los Angeles area came forward to the Marshals and identified the man in the photo as a family member.
Marshals Deputy Pat Valdenor met with the man and his family in a Los Angeles suburb. To confirm his identity, the man was fingerprinted.
"You can clearly see the difference between the fingerprints," Valdenor told ABC News. "Even without the fingerprints, there was the birth certificate, and I had his whole family in front of me - three generations. I could see it wasn't Ruffo."
The manhunt for Ruffo now continues with one less clue.
He has been on the run since 1998. The last known image now is a video of him making an ATM withdrawal in Queens, New York on Nov. 9, 1998.
Ruffo was supposed to turn himself in to serve a 17-and-a-half year prison sentence after being convicted of the scheme.
Officials say instead he drove a rental car into the long-term parking lot at John F. Kennedy International Airport and disappeared.
About $13 million of the $350 million was never recovered.
Ruffo has strong international connections and has shown a particular interest in Italy, investigators say. They believe he could be living overseas. There is a $25,000 reward for information that leads to his arrest.
Photos of the 66-year-old convicted swindler, along with possible aliases and his wanted poster are available here.
Information about submitting a tip is available here. The agency can also be reached by telephone at 1(800) 336-0102.
ABC News has been following this case for several years and documented what they've found in a new podcast series called "Have you seen this man?" There is also a documentary in the works that will air on Hulu.