Sheila, 12, and Katherine Lyon,10, shown in undated photos released by the FBI, disappeared in 1975 in Maryland in a case that went without an arrest for decades. (AP)

A former carnival worker awaiting trial in the 1975 disappearance of two young Maryland girls — Katherine and Sheila Lyon — has been indicted on a charge of rape in an unrelated case involving a then-6-year-old-girl in Northern Virginia in 1996, according to court records made public Tuesday.

Lloyd Lee Welch, 59, allegedly committed the Virginia assault aboard a houseboat in Prince William County. The indictment charges him with rape, aggravated sexual battery and indecent liberties, all felonies.

The latest charges might give authorities leverage to try to learn more from Welch about the case of the Lyon sisters, who disappeared from a shopping mall north of Washington on March 25, 1975, when Sheila was 12 and Katherine 10. For four decades, detectives made no arrest in the Lyon case.

That changed last year, when Welch was charged with two counts of first-degree murder. Detectives had found his name in old case files from the 1975 period, when he had been considered a witness, not a suspect, and re-interviewed him multiple times.

Lloyd Lee Welch, who is awaiting trial on charges of murder in the disapparance of Lyon sisters Sheila, 12, and Katherine, 10. They disappeared in Maryland in 1975. (Courtesy of Bedford County Sheriff's Office)

Snippets of the freshly recorded interrogations played in court this year in connection with the Lyon case indicate that detectives and prosecutors think Welch knows more about what happened to the girls and about others who may have been involved in their disappearance. Their bodies have not been found.

Welch has denied harming the Lyon sisters. His attorneys in the murder case — Aaron B. Houchens and Anthony F. Anderson — did not respond to requests for comment Tuesday.

The woman in the new Virginia case, now 27, described her account of an assault in an interview with The Washington Post

“I remember it very clearly,” she said. “It will never leave my mind.”

The woman spoke to The Post on the condition that her name not be used. The Washington Post generally does not identify people who report that they were victims of sexual violence unless they choose to be identified. Her account to The Post was consistent with what she has recently told investigators, according to two law enforcement officials with direct knowledge of the case.

She said she was 6 when she met Welch at a carnival with her family on the day she said he attacked her.

“He came across as a very nice person,” she said. “He plays that ‘I’m a nice guy’ very well. You would think he was someone who you could get along with and trust.”

The night of the alleged assault, she said, she went to sleep on a houseboat where she and her family lived. She said she slept on the bottom bunk of a bed, with two younger brothers sleeping on the top bunk.

She said two adults were in a different part of the boat.

She said she awoke to Welch raping her but remained silent because she was afraid he would hurt her. “I didn’t know what to do. I kept acting like I was asleep,” she said.

She said the alleged attack was not reported to the police at the time. Her accusations in the incident surfaced recently as part of the broader Lyon sisters investigation, according to the woman and law enforcement officials.

The woman said “it’s a burden I’ve had to carry. If I see someone who looks like him, it freaks me out.”

She said she thinks often about the Lyon sisters and their family and said she hopes her case can be used to find more answers for them.

“I’m hoping that they do find all the answers they are looking for,” she said.

Finding answers has been a priority for Maryland and Virginia officials overseeing the investigation.

According to authorities, when Welch was 18, he and others abducted the Lyon sisters from a shopping mall in Wheaton, killed them and disposed of their bodies on a mountain in rural Bedford County, Va.

At the time the sisters went missing, Welch worked for a traveling carnival company. He lived in the Hyattsville area of Maryland.

He had burglary convictions in 1978 in Montgomery County and in 1982 in Prince George’s County. Later, in South Carolina, he pleaded guilty to grand larceny and to molesting a 10-year-old girl.

Then, in Delaware, he pleaded guilty to molesting another 10-year-old girl. “An outrageous criminal history,” Delaware prosecutor Susan Purcell characterized his record in court in 1998.

In the Lyon sisters’ case, detectives combing case files several years ago came across Welch’s name in a report from 1975. They studied his statements, and tracked him to a prison in Delaware where he was serving time on the molestation case and interviewed him during repeat visits.

On the basis of what they heard, detectives said in court records, they concluded that Welch and others had disposed of the girls’ bodies in Bedford County. A grand jury in Bedford indicted Welch last year on two counts of murder in the case of Katherine and Sheila Lyon.

His trial is set for April.