This was the first time the alleged incident had been reported. It happened at a film set in Utah. He later returned to the film during reshoots in Malibu, as the girl's parents did not press charges.
The actress, now 26, asked THR not to reveal her identity. However, she said she recently hired an attorney.
Sizemore did not comment on the allegation. "Our position is 'no comment,' " his agent, Stephen Rice, told THR.
THR spoke with 12 people who worked on the film Born Killers. They confirmed that Sizemore was told to leave the set after the young actress told her parents that the 55-year-old Sizemore touched her genitals.
There were rumors on the set about what exactly happened. At the time, Sizemore denied the allegations and was dropped by his talent agency and managers.
Crew members told THR that the alleged incident happened when the film was almost finished. The cast was taking still portraits, which were important to the film's plot. At one point, Sizemore had to take a photo with the young actress, who had to sit on his lap. At this point, he allegedly touched her vagina.
"The girl was so young it was unclear to her and [later] her parents what had actually taken place and if it was intentional or not," production manager Cassidy Lunnen told THR.
"At one point her eyes got just huge, like she could've vomited," actress Robyn Adamson told THR. "I was watching her. She soon reintegrated and kept going, although she had trouble taking direction. Later, when I was told about what happened, I knew exactly what it was."
Casting director Catrine McGregor, who was the first to contact the magazine about the alleged incident, said the girl's agent told her the day after it happened that she told her mother. McGregor told THR she thinks the girl's parents decided not to press charges so they wouldn't ruin their daughter's acting career.