SIU director Tony Loparco says the arrest of Maria Farrell on April 2, 2013, by OPP Sgt. Russell Watson was lawful and he did not use excessive force.
It was the second time the SIU cleared the officer in the controversial arrest.
Farrell, who goes by the name Tonie, heard a woman screaming as she was walking by the area of Colborne Street East and West Street South in Orillia, Ont., in April 2013. She saw a woman being beaten by three people. The assailants fled when Farrell ran toward them. She then consoled the victim, who she says was clearly distraught.
When Sgt. Watson arrived at the scene, an altercation followed.
Farrell alleges Watson kicked her in the side of her knee, breaking her leg and sending her to the ground. She says he then punched her in the face and climbed on top of her, pressing her face into the concrete.
It is alleged that he and two other officers then dragged her to a police car, and had to struggle to get her in the car because her leg wouldn't bend properly, her lawyer, Angela McLeod, told CBC Radio's As It Happens last year.
Farrell initially faced charges of assaulting and obstructing a police officer. The charges were dismissed in December 2014.
She sustained injuries, including a fractured left tibia as the two struggled during the course of the arrest.
Watson was originally cleared of any criminal offence in May 2013 after the SIU concluded there were no grounds to believe he used excessive force.
The SIU says it reopened the investigation in March after a judge made critical comments of the officer in the case against Farrell for obstruction and assaulting a police officer that resulted in her acquittal. The judge said the arrest caused "catastrophic injuries" to Farrell.