In October 1986, he was found guilty of shooting dead his adoptive parents, sister and six-year-old twin nephews at the family farmhouse in Essex 14 months earlier, in order to claim a six-figure inheritance while also laying evidence to suggest his sister, a schizophrenic, had committed the murders before killing herself. This was the police's original line of inquiry and the media reported the deaths as a murder-suicide, but within weeks of the murders being committed the line of the police investigation had changed and Bamber was charged with five murders.
His trial judge said in sentencing him that he found the idea of ever seeing Bamber free again "difficult to foresee", and advised that he should serve at least 25 years behind bars before release could even be considered. Before the law lords' ruling in November 2002, Bamber was told by at least one Home Secretary that his life sentence would mean life.