An electrician has changed his plea mid-trial and admitted murdering two women in 1987 and sexually assaulting their corpses.

David Fuller, 67, pleaded guilty to murdering Wendy Knell, 25, and Caroline Pierce, 20, in two separate attacks in Tunbridge Wells, Kent police said.

The 67-year-old changed his pleas on Thursday partway through his trial at Maidstone crown court, which heard that he sexually assaulted the two women after killing them. He had admitted killing the two women but originally pleaded not guilty to murder on the grounds of diminished responsibility.

His trial heard that he also sexually assaulted women’s corpses in the mortuaries at Kent and Sussex hospital and Tunbridge Wells hospital while working there.

Knell was found dead in her apartment with severe injuries in Guildford Road on 23 June 1987.

Pierce was killed five months later, on 24 November, outside her home in Grosvenor Park. Neighbours described hearing screams from her flat on the night in question, the court heard on Monday. She was reported missing, and her body was later discovered in a water-filled dyke at St Mary-in-the-Marsh on 15 December 1987.

DNA evidence from both women’s bodies linked Fuller to their killings.

There were reports of “prowler activity” in the lead-up to both women’s deaths, with locals reporting a voyeur looking through their windows.

Fuller was arrested for murder on 3 December last year after new analysis of decades-old DNA evidence, and officers searched his home. There they found images of dead women at the two hospital mortuaries being abused by Fuller, the prosecutor Duncan Atkinson QC said on Monday.

Officers then found four hard drives with five terabytes of data storage in total attached to the back of a cupboard. “When these hard drives were examined, they were found to contain a library of unimaginable sexual depravity”, Atkinson said.

In a police interview, Fuller admitted to using Facebook to search for photos of the people he abused in the mortuary.

In relation to identifying and naming the files containing images of his offending against dead people, he said he had gone back to name them at a later stage, using the ledgers from the mortuary and identification tags on the bodies, Atkinson said.

He added: “He admitted to searching for them on the internet, including on Facebook. He claimed that this would be after the offending, rather than research before offending.”

Atkinson said these images provided evidence that Fuller committed the acts out of “sexual gratification” and not mental illness.

The home secretary, Priti Patel, said she hoped the victims’ families could “find some solace in seeing justice finally done”. Describing the case as shocking, she added: “The sickening nature of the crimes committed will understandably cause public revulsion and concern.”

A date for Fuller’s sentencing has not yet been set.