Thomas Dabrikas was arrested Friday night after police say an employee with the Massachusetts Bay Transportation Authority saw him assault the 18-year-old man.
The state's sex offender registry says Dabrikas was convicted in 1989 of rape and abuse of a child and indecent assault and battery on a child under 14 years old. The registry lists his address as Boston Common.
Dabrikas is listed as a Level 3 sex offender, meaning he's deemed a high risk to reoffend and a danger to the public.
It's not clear if Dabrikas has a lawyer. He's scheduled to be arraigned Monday in Cambridge District Court.
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