Try to get them on the stand but also try to get them to vote innocent. Then claim Investigator and accuse your target.
if they claim to be a Doctor, claim to be a Lookout and accuse them of visiting someone who was killed by the Serial Killer, since Doctors and Serial Killers are part of the same investigative result). If an Investigator lists them as having a result that includes a possible evil role, accuse them of that role (e.g. Accuse them and say that you investigated your said target and the investigative results that showed up for you were Bodyguard, Godfather, or Arsonist. If a Sheriff says your target is not suspicious, you can still claim to be an Investigator.