You are a
Naked Jogger
.
You're not a pervert, you just like the feel of fresh air on your skin. You fulfill your win condition when every mafia player is dead.
TV and newspaper reports of people's sightings of you haven't discouraged you from attending to your hobby, nevertheless you do it late at night in remote parts of town in order to avoid unnecessary attention.
Consequently it's not unusual for you to be the first to discover the location where mafia dumped a dead body after a kill. This makes people suspicious of you.
As long as you're around the forensic team finds a pubic hair at the crime scene every time a murder occurs and if a detective, cop or medical
doctor decides to investigate you he'll take a DNA sample, compare the two and find that they match.
Because you don't want to go to jail you are forced to lay bare the truth and admit to be the bizarre exhibitionist who has been haunting the, rather conservative regarding public nudity, townies with his shocking extrovertedness.
Any remnant suspicion of you fades away after the FBI's behavioral analysis unit declares that there is no way you'd fit the killer's profile which results in a confirmed townie status.
And yet nobody seems to want to vouch for your sanity so you wind up stripped of your voting power.