Tyrone Phillips, 27, was arrested by police officers outside a club last July and later diagnosed at hospital with a concussion.
In August, Phillips filed a complaint with the Office of the Independent Police Review Director (OIPRD) saying he was beaten unconscious during the arrest.
The OIPRD referred the complaint to Toronto's police department in September for an investigation and the case was sent to the SIU.
SIU director Ian Scott complained he was unable to conduct an adequate investigation for this case.
"As part of the SIU investigation, investigators requested relevant documents from the TPS (Toronto Police Service) and designated five witness officers and one subject officer. One of the requested documents was a copy of the original complaint submitted by Mr. Phillips, now in the possession of the TPS," Scott said. "Mr. Phillips had not kept a copy when he completed the complaint online and e-mailed it to the OIPRD. The TPS declined to provide a copy of the complaint to the SIU, claiming it was a third-party record.
"The SIU approached the OIPRD and requested a copy of its complaint in this matter and it, too, declined to produce a copy of the complaint to the Unit. The OIPRD has a policy of only sharing information with the affected police service."
The OIPRD doesn't disclose information to the SIU because of confidentiality issues contained in the Police Service Act, said OIPRD spokeswoman Rosemary Parker.
After the TPS refused to provide the documents, the SIU had Phillips sign a consent form to get the documents from the TPS, but the force continued to refuse to provide them.
The SIU claimed the TPS has the documents but wants an end to this investigation.
"Director Scott is wrong. The document in question belongs to the Office of the Independent Police Review Director. We are not allowed to release a document which belongs to someone else without their express permission. If Mr. Scott wants that document, he must get it from the OIPRD," said police spokesman Mark Pugash.
Scott said if the TPS chooses to provide the documents to the SIU at a later date the investigation will be reopened.