A 44-year-old prisoner has been arrested on suspicion of murdering convicted killer John Mansfield at HMP Whitemoor in Cambridgeshire.
Mansfield, 63, was found dead at the high-security prison near March on Sunday afternoon.
Police were called at about 4.10pm "following the discovery of the body of a man in his 60s", according to Cambridgeshire Police.
The arrested man is a serving prisoner at the same facility.
John Mansfield was found dead in the prison over the weekend
PA
Mansfield was serving a life sentence for the 2007 murder of his 63-year-old neighbour Ann Alfanso in Whalley Range, Manchester.
Alfanso, who had reduced mobility, was found dead by her carer in August 2006 after being stabbed approximately 20 times in the head and neck. He was sentenced to life imprisonment with a minimum term of 30 years.
In 2014, Mansfield received a second life sentence after stabbing another prisoner with a broken plate at HMP Full Sutton, near York.
A Cambridgeshire Police spokesman confirmed an investigation into the death is ongoing.
LATEST DEVELOPMENTS
- Mother jailed over Southport social media post has bid to see daughter REJECTED despite being 'ideal candidate'
- There's only one solution for the vile Islamists in our jails - let's hold a referendum says Kelvin MacKenzie
- Counter-terror police launch urgent probe after Manchester Arena bomber's brother attacks THREE prison officers in 'appalling' rampage
HMP Whitemoor
PA
A spokesman from Cambridgeshire Police said: "A 44-year-old man has been arrested on suspicion of murder."
A Prison Service spokesman added: "Police are investigating the death of prisoner John Mansfield at HMP Whitemoor on Sunday April 13....It would be inappropriate to comment further at this time."
Steve Gillan, general secretary of the Prison Officers' Association (POA), described the incident as "appalling news" coming after serious assaults at Frankland prison over the weekend.
He said: "This is appalling news on the back of the serious life-threatening assaults at the weekend in Frankland prison...To have a death which is being treated as a murder investigation and now subject of a police investigation confirms everything the POA have warned about."
He added: "The POA will not add anything as the police are investigating but suffice to say these are concerning times in the prison service."
The incident at HMP Whitemoor occurred alongside another violent prison attack at HMP Frankland in County Durham, where three prison officers were assaulted with hot oil and homemade weapons.
Prime Minister Sir Keir Starmer said he was "appalled" by the attack at Frankland.
A Downing Street spokesman said: "The Prime Minister is appalled by the attack that we saw at the weekend and his thoughts are with the officers involved. Prison staff work around the clock to keep the country safe and we will never tolerate the violence that is targeted towards them."
Shadow justice secretary Robert Jenrick urged the government to 'get a grip'
PA
Shadow Justice Secretary Robert Jenrick criticised prison management in a post on social media.
He said: "Governors and the Ministry of Justice have lost control...It's time they got a grip."
The Ministry of Justice has said it will carry out a review following the attack at HMP Frankland, and has suspended access to kitchens in separation and close supervision units, where inmates are kept apart from the general prison population.
