TORONTO - Toronto's police chief is questioning the way the province's Special Investigations Unit handled some complaints into police actions during the summer's G20 protests.

The unit released its findings last week, after looking into complaints from six people who allege police officers injured them during the summit.

The SIU concluded there were no grounds to justify laying criminal charges against officers in any of the cases.

But Chief Bill Blair says in one case, the SIU directed people to a video posted on YouTube, saying it corroborated an allegation against police.

Blair says the video was forensically examined over the weekend and found to be "tampered with" -- meaning it was edited and audio and video removed.

The chief says the incident raises questions about the quality of the SIU's investigation, since the parts that were cut out could help explain why the man was arrested and why force was used.

"For the SIU to rely on a YouTube video as corroboration of an allegation against a police officer, a video that has clearly been tampered with, a video they appear not to have examined very closely, raises serious questions about the quality of their investigation," Blair said in a release Monday.

"They have been entrusted with a very important job. Their mandate, as an independent agency, is to examine serious allegations against police, investigate them thoroughly, professionally and objectively. That does not appear to have been done in this case."

In several cases the SIU did not dispute that officers probably used excessive force. But the agency said that since individual officers could not be identified, no one could be sanctioned.

More than 1,000 people were arrested during the summit. Of that group about 300 were charged and five months later, few are still facing those charges.