Waterloo Regional Police have been called in to probe how Toronto Police handled the alleged beating of a young man by one of its officers.

Toronto Police chief Mark Saunders announced on Thursday that Waterloo police will be responsible for an internal investigation into the circumstances surrounding the alleged assault of Dafonte Miller, 19.

The internal probe — known as a "Section 11" investigation — is mandatory, Saunders said, but the involvement of another police force is not.

"With the conclusion of the [Special Investigations Unit] investigation, normally, I would conduct a Section 11 investigation. However, in light the circumstances now before me, I have taken the extra step of reaching out to an independent agency to complete the Section 11 investigation," Saunders read from a prepared statement at a Toronto Police Services Board meeting.

'There have been serious allegations made'

Saunders told the board that he has contacted Waterloo Regional Police and their officers will look into the "procedures, policies, governance and conduct" of Toronto police as they relate to the alleged beating of Miller.

"This case is complicated and there have been serious allegations made, which everyone is taking seriously, especially the members of the Toronto Police Services Board," board chair Andy Pringle said at Thursday's meeting.

Chief Mark Saunders announced on Thursday that he is bringing in Waterloo Regional Police to conduct an investigation into how Toronto Police handled the alleged assault of 19-year-old Dafonte Miller. (Barry Smith/CBC)

Toronto Police Const. Michael Theriault, who was off-duty at the time of the incident, has been charged with aggravated assault, assault with a weapon and public mischief in connection with the case.

Miller was allegedly chased down a street and hit repeatedly with a steel pipe by two men in Whitby in December 2016. The case was was initially investigated by Durham Regional Police.

Miller suffered a broken nose, jaw and wrist and is awaiting surgery to remove an eye injured in the incident.

The Special Investigations Unit, a police watchdog, has also charged Theriault's brother Christian Theriault, who is not a police officer.

SIU notified months after incident by lawyer

Saunders confirmed on Wednesday that the Toronto Police Service was informed of the incident after it occurred, but neither Toronto nor Durham police notified the SIU.

The SIU was notified on April 27, when Miller's lawyer contacted the province's police watchdog.

Saunders told the police services board that it was the responsibility of Durham police to contact Toronto police because the incident involved Theriault., an officer.

It appears from Saunders's statement that contacting the SIU was then in the hands of Toronto police.

"As per protocol, members of my Professional Standards Unit applied the policy regarding SIU involvement with the facts they had at that time. They made their decision not to contact the SIU based on that information," he said.

Waterloo police confirm they will run probe

In a statement from Waterloo Police Chief Bryan Larkin, the force confirmed that it will conduct the investigation into the Miller case. But it would not comment on the Section 11 investigation, directing inquiries to Toronto police.

Speaking outside of the Toronto Police Services Board meeting, Mayor John Tory, who is a board member, said there are still many "unanswered questions" about how this case was handled. But Tory is waiting until the independent probe is complete.

"I think what we have to do is let the Waterloo police service do their job," the mayor said.