The investigation by the sheriff's office in 2009 reveals Bates received special treatment and equipped his personal vehicle as a police car.
According to the investigation report obtained by News On 6, the deputy overseeing Bates' training says he signed off that Bates had 150 hours more training than he actually completed.
Bates is charged with manslaughter for shooting unarmed suspected illegal gun dealer Eric Harris on April 2, 2015.
The report from 2009 claims there were red flags right from the beginning. It states when Bob Bates "started operating at the advanced [reserve deputy] level, several other reserves voiced their concerns."
The report says a sergeant tried to suspend Bates for failing to meet firearm qualifications, but Major Tom Huckeby and then-Deputy Chief Tim Albin stepped in, saying that was "harassment."
When deputies questioned Bates about using his personal car to make unauthorized vehicle stops, the report quotes Bates as saying, "Well I can do it and if you don't like it you can talk to...Sheriff Glanz."
Another internal memo from 2008 says Bates, "...has not completed the 480 hour [training] and is not authorized to make traffic stops."
In the 2009 report, Bates' field training officer, Warren Crittenden, said Bates was not ready for the field, saying Bates wasn't good at "traffic stops and operations."
Crittenden was later fired from the sheriff's office and is currently in jail facing murder charges.
The report concluded, "Policy has been violated and continues to be violated by...Huckeby and...Albin with regard to special treatment shown to...Bates."
Albin could not be reached for comment.
Huckeby referred us to sheriff's office spokesperson Major Shannon Clark, who would not comment.
Tulsa County Sheriff Stanley Glanz discounted the investigation in a Monday briefing:
Glanz: "There was an investigation that occurred under Sheriff Edwards."
Reporter: "What was the outcome of that?
Glanz: "I'm not sure. I believe that they found that there was no special treatment."
Former Undersheriff Brian Edwards, who led the 2009 investigation, says he now remembers it, but won't talk about it.
The sheriff's office released a statement late Friday afternoon.
Their attorney said the release of the special investigation documents was unauthorized and they are looking into how it happened.
The sheriff's office said the document demonstrates its willingness to investigate and review allegations of policy violations.