Eubanks, who soon became a suspect in the case, was convicted of Mary Ellen’s murder in May 1966 and sentenced to death. His sentence was commuted to life in prison in 1972, when the Supreme Court ruled the death penalty unconstitutional.
A year later, Eubanks obtained his freedom in his escape, which was described by the Marshals Service as one of the most notorious in Ohio history.
A $25,000 reward is being offered for information leading to his capture.
"While the Eubanks' case is designated as a cold case, I want to assure the public our investigation into his whereabouts is very active," U.S. Marshals Service Deputy Director David Anderson said in the news release. "I have total confidence in our deputies and our law enforcement partners, who are determined to make sure Eubanks' last days are spent in a prison cell, where justice intended it."
Deener's sister, Myrtle Carter, told the News Journal that their mother sent Mary Ellen and their 12-year-old sister, Brenda, to the laundromat by cab after the family's dryer broke down.
"The reason she was so comfortable (sending the girls out at night) is my grandmother lived next door to the laundromat," Carter told the newspaper.
When the girls ran out of change, Mary Ellen left Brenda there and went out on her own to get what they needed from another laundromat, the News Journal reported. She never returned.
Brenda went next door to their grandmother’s house when her older sister didn’t come back for her. Their grandmother, who began searching for the teen, had to identify her body for police.
The newspaper reported that Eubanks was out on bail on an attempted rape charge when he abducted and killed Mary Ellen Deener. The previous charge stemmed from an attack on an 18-year-old waitress.
"He's an absolute monster," Deputy U.S. Marshal David Siler told the News Journal. "If you saw the size of the guy compared to the size of this little girl, she never had a chance."
Siler, who has worked the case since January 2016, said in the marshals’ news release that he thinks about the case -- and specifically Deener -- every day.
"In law enforcement, there are cases that keep you up at night," Siler said. "This is one of those cases."
Carter told the News Journal that her mother, who died in 2000, was never the same after losing Mary Ellen. Brenda, who was close to her older sister, was also tormented throughout her life by the loss.
"I think she never, ever got over it," Carter said.
Brenda Deener died in 2014, her sister's murderer still at large.
Marshals believe Eubanks is still alive and living under an alias. He could be living under the alias Victor Young, the news release said.
Leads over the years have placed him in California and Michigan, but his current whereabouts are unknown.
"Lester Eubanks has had a lot of time on the lam," Siler said. "Fugitives on the run as long as Eubanks tend to use that time to change their appearance, use aliases, and even start new lives. He literally could be hiding in plain sight. This is why we are asking citizens to be vigilant and contact us with any information they believe will help us apprehend him."
Eubanks is described as a black man who is 5 feet, 11 inches tall and, at the time of his disappearance, weighed approximately 175 pounds. He also had a mole under his left eye when he vanished.
Anyone with information is urged to contact the nearest U.S. Marshals office or the U.S. Marshals Service Communications Center at 1-800-336-0102.