Officials began investigating after a woman came to Bridgton Hospital and said she was raped at a Newry home in the early morning hours of April 2, Oxford County Sheriff Wayne Gallant said.
Witnesses told investigators that Johnston was inside a room at the home during the assault. People confronted Johnston at the house and he quickly left, officials said.
He was last seen that same day at 1 p.m. when he checked out of a Sunday River hotel.
Johnston’s family reported him missing on Monday, April 3 after he never returned from the trip.
Police put out a missing person notice April 6 and Johnston was found dead in a wooded area in Auburn a few hours later.
A medical examiner ruled his death a suicide.
Officials said Johnston was the only suspect in the case. He and the victim had no known relationship before the assault, officials said.
Officials are awaiting DNA results but said the case is closed.
Johnston worked at Action News Jax in Jacksonville, Florida, until 2014. He'd been working as a meteorologist at the NBC affiliate in Portland, Maine before his death.