Marin alleged the tweets, which linked the ombudsman with al-Qaeda, were coming from a Durham Regional Police officer.
Firing back on Twitter, Marin eventually named a specific officer, and disclosed that officer's salary.
Marin got the police board correct, but the man he named does not have any knowledge of the rogue Twitter account, Durham Regional Police said Monday.
An internal investigation into inappropriate tweets made to the ombudsman and Toronto Coun. Janet Davis will result in disciplinary action against a different Durham officer.
"Scott Dennis," the officer Marin originally suspected, was on annual leave, and has been cleared in the case. But it was subsequently determined the Twitter account had been opened by a fellow police officer.
Durham Regional Police intend to charge the officer under the Police Services Act. But he is not suspended and will remain on duty until a forthcoming hearing.
"With very few rules and even less accountability in the world of social media, it's not the first time someone has landed in hot water. Politicians and celebrities are usually the culprits. This is a first for us here at the DRPS," said Chief Constable Mike Ewles said in a statement released on Monday.
Police said several attempts were made to contact Marin, though none have been successful.
"First and foremost, I am concerned that one of my police officers allegedly used a fellow officer's information to create a fictitious Twitter account and then use it for such offensive purposes. That officer will be held to account," Ewles said.
But the chief constable also said it was "troubling... that a high-ranking public official like the Ombudsman of Ontario would rush to judgment and identify any person, without the benefit of some sort of objective investigation and evidence, particularly given Mr. Marin's experience."
Ewles said that the officer who was named by the ombudsman "is an outstanding police officer who has had his personal and professional life turned upside down for no reason."