A former Massachusetts police detective was convicted Tuesday of strangling a 23-year-old pregnant woman he had been sexually abusing since she was 15 — and the only reason he faced justice is because the feds stepped in after local investigators rushed to call it a suicide and close the case.

Matthew Farwell, 40, met Sandra Birchmore when she was just 12 and enrolled in the Stoughton Police Department's youth Explorers program, where he was an instructor. Prosecutors said he began sexually assaulting her at 15. He killed her on Feb. 1, 2021 — the day before his wife gave birth to their third child — after a tipster reported their relationship to his department and Birchmore told him she was ready to come forward about the abuse.

The institutional failure is staggering. Massachusetts State Police investigators, some with personal connections to Farwell, concluded within days that Birchmore killed herself. One investigator, according to Assistant U.S. Attorney Brian Fogarty, saw nothing suspicious and dismissed her as a