A suspicious ballot paper was seized after a would-be voter in the Edinburgh Northern and Leith constituency tried to vote, only to be stopped because someone had already cast a ballot in their name.
Candidates and polling agents were summoned on Saturday morning as counting got under way in Edinburgh to witness count staff and police attempt to track down the vote in question.
Depute returning officer Chris Highcock confirmed that the vote allegedly cast in someone else's name - a crime known as personation - had been located and was being investigated by police.
The votes cast in another person's name will still be counted in the final tallies in case it turns out to be genuine, Mr Highcock told the PA news agency, but it has now been removed and placed in an evidence bag should police need to test for fingerprints.
The person who was unable to vote would have been able to secretly write who they intended to vote for in a sealed envelope which could then be revealed in the event of a legal challenge or court case, he said.
The potential case of electoral fraud occurred at St Serf's Church in Ferry Road, Inverleith, on polling day.
Speaking to PA, Mr Highcock said: "In this case, it looks like someone has turned up pertaining to be somebody else and they have been issued with the vote having said 'Yeah, I'm that person'.
"In cases like that, it's important to the police because it's a crime to pretend to be somebody else and get their vote.
"What happens then is that the ballot paper is traced, the ballot paper is taken out (of) the box, it is put in an evidence bag and the police hold that and they do an investigation, to try and find out who it was and see what happened."
He added: "Because it involves the ballot box, we've got to have candidates, agents and police there, so as we did that there were lots of people watching and it was in full view of any observers who need to be there."
Reporting by PA