A man who strangled a teacher before having sex with her dead body told prison staff he wanted to kill again to prove he was “mentally ill”, a report reveals.

Carl Langdell, 31, was on remand at HMP Frankland, for slaughtering Katie Locke, 23, when he made the disturbing admissions, before later taking his own life.

He also told healthcare experts he was receiving “subliminal messages” and tried to harm himself in an attempt to show that he had a “psychotic” disorder.

But a Prison Ombudsman report showed he was transferred to HMP Wakefield, dubbed the ‘Monster Mansion’, after doctors decided he was trying to “fabricate” a mental illness.

Langdell's behaviour “deteriorated” at the notorious prison - where he was serving a 26-year sentence - and he later made threats to “kill anyone” who walked past him.

And he eventually died in February 2021 after guards found him with self-inflicted cuts to his neck inside his cell, a day after he declined to take part in his victim's inquest.

Langdell, from Buckhurst Hill, Essex, murdered Katie Locke, who he met on the dating app, ‘Plenty More Fish in the Sea', on Christmas Eve 2015.

But just a month later, he claimed he was ready to take another life to prove his psychosis while on remand at HMP Frankland, County Durham, the report revealed.

It said: “In January 2016, while on remand at HMP Frankland, Mr Langdell told healthcare staff that he would prove he was mentally ill by killing someone, before taking his own life.

“He later harmed himself by cutting and needed hospital treatment. Mr Langdell was also violent on several occasions and assaulted officers.

“He was diagnosed with emotionally unstable, dissocial and obsessive-compulsive personality disorders.”

In March 2016, after he was sentenced to 26 years imprisonment for murdering Katie Locke, he told doctors he had been receiving “subliminal messages.”

But these were dismissed by psychologists as “fabricated delusions”, and he was later sent to HMP Wakefield in 2019, where he was expected to complete his sentence.

The report said: “In June 2016, Mr Langdell reported that he was receiving subliminal messages, described delusional ideas and reported psychotic symptoms.

“A psychiatrist at Frankland referred Mr Langdell to Rampton High-Security Hospital and he was transferred in July 2017.

“In hospital, Mr Langdell made further significant attempts to harm himself and threatened to harm staff.

“After treatment at Rampton, a hospital psychiatrist concluded that Mr Langdell did not have a psychotic illness and had fabricated delusional thoughts and recommended that he should continue to serve his sentence in prison.

The report said that in 2021, two years into his sentence at HMP Wakefield, he had made further threats to “kill” anyone who walked past his cell.

It said: “On 21 January, Mr Langdell’s behaviour deteriorated, he spat at anyone who walked past his cell and shouted that he would hurt or kill anyone who went into his cell.”

And just after midnight on 11 February 2021, he was found with cuts to his neck, and later pronounced dead at 1.47 am.

Langdell, from Buckhurst Hill, Essex, was convicted of murdering Katie Locke, who he met on a dating app.

He had lied to her about being a lawyer, and even set up a fake Linkedin account, before luring her back to a hotel room during a first date and carrying out his depraved attack.

Langdell later phoned hotel staff to ask for a late check-out and left a “do not disturb” sign on the door.

Police later found he had used a laundry trolley to dump Katie’s body in the grounds of the hotel, in Waltham Cross, Herts.