SERGEANT Brendan Thomson was so scared of retribution for blowing the whistle on the Australian Federal Police he went to extraordinary lengths to protect himself. He fastened his locker with luggage straps and tamper-proof forensic tape to protect himself from senior officers who he feared could stitch him up by planting something incriminating. He thought that was a likely payback for going over the heads of his bosses. Sgt Thomson says he's now engaged in a very personal war with the force he was devoted to for 14 years. The trouble began in November 2010. It was then that he dared to directly email AFP Commissioner Tony Negus over concerns the impending withdrawal of his six-member riot squad from the Christmas Island detention centre would put the lives of asylum seekers and locals at risk. He warned the detention centre was a ticking time bomb and immigration staff, along with the centre's operator Serco and remaining 32 AFP officers, didn't have the specialist skills to deal with riots. He felt his many warnings to his direct superiors had not been heeded. But within an hour of shooting off his email to Commissioner Negus, it was forwarded to them. The withdrawal went ahead, and four days after the email was written, Sgt Thomson was removed from operational duties. He was soon facing a misconduct charge for breaching a directive, sent to offshore AFP officers, not to directly contact the commissioner over operational problems. Sgt Thomson says his is a classic tale of a whistleblower being punished for acting and speaking out. The AFP says it's no such thing and maintains the withdrawal of the squad was justified. Sgt Thomson struggles with that assessment. Three-and-a-half months after he emailed the commissioner to warn chains of command were failing and that the detention centre was at risk, his "I told you so" moment came. In March 2011, the Christmas Island facility erupted in an explosive riot. For six long days authorities struggled to regain control. Asylum seekers set fire to buildings and fled. Some walked 18km into residential areas and laid siege to the island's airport. In May this year, Sgt Thomson went public about his previous warnings about the security situation at the detention centre. He says he doesn't regret turning whistleblower, but it's come at a very heavy price. From the moment he began warning his superiors back in November 2010, he says he's faced a covert campaign of intimidation, been ostracised, and faced threats from management for upholding his oath to protect lives and property. He says the AFP has invented issues about his service, ranging from excessive overtime to unjustified claims for work expenses. "Mud sticks, and it was getting shovelled on me from the top," he told AAP. In May 2011, with his anxiety reaching a tipping point, Sgt Thomson lodged a formal complaint with the AFP about his treatment. At his desk in Canberra, he sealed his locker, filing cabinet, weapons cases and bags with luggage seals and tamper-proof evidence tape. He began working from home. "I was really concerned I could end up with something in my locker that shouldn't be there," he said. It was clear there wasn't anything they wouldn't do to try to discredit me. By April 2013, he was declared a possible integrity risk. Colleagues were asked to document any contact they had with him, as they were required to do with drug users or known criminals. Two-and-a-half years on from his initial warnings about the detention centre, Sgt Thomson has been diagnosed with a work-related stress condition and is on leave without pay. He's spent $210,000 on ongoing legal battles related to his loss of income and his treatment. He says he wants to affect change in the AFP culture, and make the hierarchy accept that dissent is not defiance. The oath he took when he became an officer is also at the forefront of his mind. "Once police abandon their obligations to the rule of law, then the whole place falls apart," he said. In the last sitting days of the current federal parliament, new laws were passed offering historic levels of protection for whistleblowers employed by the Commonwealth, including AFP officers. During final debate on the legislation, Greens Leader Christine Milne said the AFP had a problem. "AFP senior management are more in denial that a problem exists rather than being willing to accept that the culture needs to change," she told the Senate. For its part, the AFP says the force has a well-established integrity framework and protects, rather than punishes, whistleblowers. It says Commissioner Negus immediately sought further advice in relation to Sgt Thomson's warning, but wouldn't clarify if it was just his direct superiors who were turned to. Deputy Commissioner Peter Drennan told AAP briefings provided by Sgt Thomson were considered by the AFP in deciding on the fate of his squad on Christmas Island. He said independent external reviews had not criticised the withdrawal, despite the violence which followed. "The AFP has not and would not make an operational decision that would imperil the safety of the community or its offices," he said. Mr Drennan said the AFP had done all it could to help Sgt Thomson, including granting him additional leave entitlements. The AFP says efforts to resolve the dispute had also been rebuffed. "The AFP totally and completely rejects Sgt Thomson's assertion that any member of the AFP would take any inappropriate, vindictive or unlawful action against him," a spokesperson said. The assertion that the AFP senior management would 'plant' illicit goods on Sgt Thomson is ridiculous and without foundation or precedent.