Anthony "Tony" Armstrong was born Anthony Wilkinson on June 30, 1962, in Easington, a town located in County Durham, England. He spent much of his life in the surrounding areas of County Durham and Cleveland. In August 1993, he moved into a council-owned flat on Frederic Street. In later years, he adopted the surname of his stepfather, George.

Throughout his life, Armstrong struggled with unemployment and had issues with alcohol and prescription drug use. He had a long history of criminal convictions. Although he was investigated for sex offenses against children, he was never formally charged. Mental health professionals diagnosed him with a personality disorder and a psychopathic personality.

To secure housing, Armstrong's psychiatric consultant wrote a letter to the Housing Department stating that he was vulnerable. Despite this, people in his neighborhood viewed him with disdain and distrust. They often referred to him as "Tony the Pervert." 

On 30 June 1994, Anthony "Tony" Armstrong was celebrating his 32nd birthday. That afternoon, he returned home by taxi around 15:30, which was about the same time that three-year-old Rosie Palmer approached a local ice cream van. After getting an ice pop, she was abducted by Armstrong as she walked away from the van. Her stepfather, John Thornton, began to search for her two hours later when he noticed she was missing. At 20:45, Rosie was formally reported missing to the police.

The investigation included extensive searches in the area. Detective Superintendent Doug Smith and his team conducted door-to-door inquiries and used tracker dogs to help locate Rosie. Armstrong's flat was inspected for the first time on 1 July 1994. Police returned to his residence on 2 July for further searches. By 3 July, Armstrong was approached by detectives who noticed changes in his behavior, becoming nervous and shifty. Suspecting him, the detectives arrested Armstrong. During a second search of his flat, they discovered Rosie's mutilated body hidden under a settee in the loft.

Armstrong initially denied any involvement, claiming someone else had placed the body there. However, he was charged with murder and remanded in custody. While on remand, Armstrong wrote a letter to crime author Bernard O'Mahoney, admitting to the murder and detailing his plan to feign mental illness to plead for a lesser charge. This letter was shared with the police and presented as evidence during his trial. He later changed his plea to guilty.

On 28 July 1995, Armstrong was sentenced to life imprisonment for the murder of Rosie Palmer. The judge did not set a specific minimum term for parole but, in a subsequent ruling in 2006, the minimum term was set to 16 years, making him eligible for parole in July 2010. Armstrong faced several challenges regarding his release. In March 2023, his seventh application for parole was rejected, and the Parole Board decided he would not be reconsidered until at least 2025. At that point, he would have spent over 30 years in custody.