MIAMI — An Orlando woman now in her mid-20s told investigators that George Zimmerman, who is charged with second-degree murder in the killing of Trayvon Martin, molested her for more than a decade, beginning when they were both young children, according to an audio tape released Monday.

The woman, whose parents were close to the Zimmerman family, talked to investigators on March 20. Identified only as Witness 9, she said she had come forward now, a decade after her last encounter with Zimmerman, 28, because, after his arrest, she was no longer afraid of him.

It is unclear how, or whether, prosecutors plan to use the allegations in their case against Zimmerman, who is free on $1 million bond.

Mark O’Mara, Zimmerman’s lawyer, tried unsuccessfully to block the special prosecutor from releasing the tape, which he said was irrelevant and prejudicial. He also sought to block the release of another tape in which the same witness describes Zimmerman’s family as routinely disparaging black people.

The witness said that Zimmerman, who is about two years older than she is, first molested her when she was 6. She was staying in the Zimmermans’ Virginia home while her mother and father were moving from Louisiana to Orlando. The woman said Zimmerman had groped her with his hands while they lay under a blanket as they watched television with a group of children.

Allegations Revealed

Other groping episodes followed, she said. She visited the family ‘‘at least once a year’’ and she was molested during some of those visits, she said, including once behind a curtain when she was 7 or 8 years old and another time on a bunk bed when she was around 12.

‘‘Before we left the room or left any place, he would say we weren’t doing anything — we were just laying there or we were just playing hide-and-seek,’’ said the woman, whose voice cracked as she recounted the events. ‘‘He would always make sure that he told me that. And I didn’t know. I was a kid. I didn’t know any better.’’

The acts typically involved ‘‘a lot of kissing, groping. He would put his hands under my shirt and just rub and grab my chest and put his hands down my pants again,’’ the woman said. The woman said that she had been traumatized by what happened and that she had blocked much of it from her mind. She said she had been too ashamed to tell anyone. But she said she also feared that no one would believe her because Zimmerman came across as so likable.

The last encounter, the only one that took place in Florida, occurred after Zimmerman arrived in Lake Mary, not far from where she lived with her family, the woman said. She was 16 and Zimmerman was 18. He had invited her to a housewarming gathering, she said.

When she arrived inside, he was alone. Frightened, she said, she followed his instructions and lay down on the bed, and he started groping her again. At that point, she said, she got up, ran out and jumped into her car. He followed her to the door but no farther, she said. Always, she said, ‘‘I was so afraid.’’

In 2005, when the woman was 19, she confided in her sister who told their parents, she said. She and her parents met with Zimmerman in Lake Mary, she said. But she never described to them the full extent of the molesting, she said.