The last known person to see Sandra Birchmore alive was a police officer.

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He acknowledged having sex with her when she was 15, according to a court ruling citing the officer’s text messages. That document indicates that his twin brother — also an officer and Explorer mentor — and a third Stoughton officer, a veteran who ran the program, eventually had sex with her, too.

These assertions, disclosed in an internal police investigative report and through an ongoing lawsuit filed by Birchmore’s family, have sparked demonstrations and an online petition asking for further investigation into her death. The three men, who did not respond to requests for comment, have denied any wrongdoing and have not been charged with a crime.

The youth program that introduced Birchmore to the officers is among hundreds of such chapters at police agencies around the country. Created by the Boy Scouts of America decades ago, law enforcement Explorer posts are designed to help teens and young adults learn about policing.

Birchmore’s case is among at least 194 allegations that law enforcement personnel, mostly policemen, have groomed, sexually abused or engaged in inappropriate behavior with Explorers since 1974, an ongoing investigation by The Marshall Project has found. The vast majority of those affected were teenage girls — some as young as 13.