A “bloodthirsty” couple planned and conducted the murder of a 38-year-old woman and then dismembered her body, a court has heard.

Steven Sansom, 45, from Sutton, and Gemma Watts, 49, from Croydon, have both pleaded guilty to murdering Sarah Mayhew last year and perverting the course of justice.

Sansom had previously served nearly 20 years for the murder of taxi driver Terence Boyle in 1998.

At their sentencing hearing at the Old Bailey on Thursday prosecutor Tom Little KC said that it was a murder that involved sexual and “sadistic” conduct.

Warning: The following material contains references to sexual violence may cause distress.

Before the murder the defendants had exchanged “depraved” messages indicating a desire to kill victims with a knife or knives while engaged in sexual activity.

Sarah Mayhew had accompanied Sansom to his flat in Burnell Road, Sutton, at about 23:00 GMT on 8 March 2024, the court heard.

“From that point in time she was never seen again and she never left that property alive,” said Mr Little.

“How long she lived for only the defendants know and they have never said.”

“What precisely happened to her body after she had been murdered by them in the property only the defendants know,” Mr Little added.

Sarah Mayhew’s head and limbs were found over eight miles (nearly 13km) away in Rowdown Field in New Addington on 2 April, the court heard.

Her torso was discovered later in the River Wandle.

Sarah Mayhew was living at Friars Wood in Croydon at the time of her death and knew both Sansom and Watts, Mr Little said.

Messages between the defendants indicated that Sarah Mayhew introduced them to each other in the summer of 2023.

And by the time of the murder the defendants had been in a sexual relationship for seven months.

“Messages indicate that from the early stages their relationship was characterised by sado-masochistic violence,” said Mr Little.

“Such was the intensity of the defendant’s relationship at this early stage that they referred to dying together if they were ever caught,” Mr Little added.

Sarah Mayhew must have been killed or incapacitated inside Sansom’s flat on the night of 8 to 9 March 2024, the court heard.

“Given the messages sent between the defendants in the months before it is not credible, the prosecution submit, to conclude that she was killed immediately.”

After the event Sansom had tried to justify what they had done by stating: “We’re not evil, we’re not evil. We done the world a service.”

The judge, Mrs Justice Cutts, is expected to pass sentence on Sansom and Watts on Friday morning.