A cancer-riddled murderer was found dead in his HMP Frankland cell.
Guards discovered Sibigam Ekprikpo "lying on the bed, staring at the ceiling with his mouth open" during morning checks.
The 65-year-old was serving his life sentence at the notorious County Durham prison - nicknamed 'Monster Mansion' - for his role in the slaying of a strip club bouncer.
The Old Bailey heard Ekprikpo had waited for doorman Bogdan 'Tony' Paduret to leave work at London's Mayfair Club in November 2010.
He then tipped off the organiser of the killing, which led to the fatal gunshots being fired.
He helped plot the murder as the bouncer had shown "disrespect" to pals by not letting them inside the club weeks earlier.
A judge ordered Ekprikpo serve at least 25 years behind bars.
However, a newly published Prisons and Probation Ombudsman report revealed that Ekprikpo was already battling prostate cancer before he was locked up.
He'd been diagnosed with the disease in 2009. and over the next decade, it spread through his body.
The report said: "On April 1 2019, after Mr Ekprikpo had a CT scan, a consultant oncologist confirmed that the cancer had spread to his bones.
"He decided that Mr Ekprikpo should receive palliative treatment.
"Mr Ekprikpo’s health remained fairly stable but when it deteriorated on April 15 2020, he moved to the healthcare inpatient unit so that healthcare staff could monitor him more closely."
Just two days later, a member of staff looked through his cell panel and noticed he was unresponsive.
"When he looked through Mr Ekprikpo’s cell observation panel, he saw that he was lying on the bed, staring at the ceiling with his mouth open," adds the report.
Staff, including nurses, rushed to his side while an ambulance was called but Ekprikpo was declared dead soon after.
However, the watchdog raised "concern" that a paramedic had to confirm his death - as nobody present at the Category A was trained to do it.
Since his death, the report states that six staff have been trained to confirm the death of inmates.
The Ministry of Justice has been approached for further comment.
