investigation shows colleagues expressed concerns about robert bates .
probe reveals he was not given special treatment during his application .
however report in 2009 says he was once he was employed in tulsa .
supervisors allegedly intimated colleagues to benefit bates .
he has been charged with second-degree manslaughter in relation to the death of eric harris in tulsa , oklahoma , on april 2 .
district attorney steve kunzweiler has begun contacting outside law enforcement agencies for further investigation .