Officer Barnes was the police officer that was assigned to question Claire after her car crash. He met her in the hospital where she was staying and he asked her several routine questions concerning the accident. Claire, who felt that it was her fault that her mother was injured, got angry and extremely defensive during his questioning, and he apparently took offense. He implied that Claire's mom was going to die, and he left her alone in her hospital room. ("Par Avion")
On his sleeve badge is "State Police". The Police are organized differently in Australia than the USA. Police in Sydney are not "Sydney Police" or "State Police", they are "NSW Police" (NSW = New South Wales, which is a state of Australia like Florida is a state of the USA). The badge is nearly identical to the NSW Police badge.