Anyone can use this trick. A maniac who has accurately calculated the player and decided to pretend to be an investigator; a Mafia member with the rest of the team, who decided to sacrifice one of their own in this way, but at the same time, if they all do it skillfully, they will get a 100% alibi. So there's no need to freak out. Everything is within the rules. The Mafia are only exposing themselves more now.