Axe murderer got the wrong woman: court A MAN who murdered a prostitute in a brutal axe attack believed she was his ex-wife and "killed the wrong person," a NSW Supreme Court judge has been told. David John Dunn, 28, was suffering from a delusional disorder when he murdered Rebecca Apps, 28, at Barrack Heights, near Wollongong, on September 9, 2010, his lawyer told told the Supreme Court in Sydney on Thursday. Dunn has pleaded guilty to murdering Ms Apps, a street sex worker, and to armed robbery. Ms Apps' mother, Christine Bennett, told Dunn's sentence hearing the light went out of her life when she heard her daughter had been murdered. David, I don't know why you did what you did. I probably never will," Ms Bennett told her daughter's murderer, who sat doubled over in the dock for most of the hearing. But you have taken away one of the greatest treasures God ever gave to me. Ms Apps' sister, Heather Bennett, described her sorrow at not being able to view her sister's mutilated body following the "brutal attack." "David Dunn took away my last goodbye," Heather Bennett said. My sister was an amazing, beautiful, delightful person and should be here today. Forensic psychiatrist, Dr Gerald Chew, said Dunn suffered from a delusional disorder, a mild intellectual disability and poly-substance dependence. The court was told he was suffering from a delusion that his ex-wife had killed two of his family members. He told a psychiatrist he saw tattoos while having sex with Ms Apps that made him believe she was his ex-wife and so he attacked her. "He now knows that his belief that the deceased was his ex-partner was wrong," Dr Chew told the court. (He told me) he was sorry about it because he was quite clear to me his intended target was the ex-partner. Justice Christine Adamson noted that in his initial interview with police, Dunn did not mention his ex-wife, but said he was "embarrassed and frustrated by his impotence and responded by killing her." Dr Chew said this was an "unlikely scenario." Defence barrister Mark Ierace, SC, said Dunn's delusional disorder was "at the heart of the attack." "He killed the wrong person and there was still an intention to kill," Mr Ierace said. The delusion has disappeared, all too late in terms of saving the deceased, but that is gone. Crown prosecutor Lou Lungo said aggravating factors included Dunn's attempts to dispose of Ms Apps' body along with clothing and the axe. Justice Adamson noted Dunn would be facing a long custodial sentence. He will be sentenced at a later date.