A prisoner who was stabbed to death at Wormwood Scrubs has been named by police as Saleh Khader.
Four men were arrested today (1 February) on suspicion of murdering the 25-year-old inmate who was found with stab wounds at the west London jail yesterday afternoon.
Two men both aged 21, a 20-year-old and a 23-year-old man, who are all prisoners at the jail, remain in police custody.
Police and paramedics were called to the prison on Wednesday afternoon but Khader was pronounced dead at the scene despite medical assistance.
The Met Police said his next of kin had been informed and a post-mortem examination would be held. The Homicide and Major Crime Command was investigating.
Wormwood Scrubs is a Victorian-built Category B prison, which holds up to 1,279 adult males. Records from last month show that 1,131 prisoners were being held.
An inspection report published in December found that the jail suffered chronic staff shortages, food supply issues and a surge in violence.
HM Inspectorate of Prisons inspectors found areas of the jail were scattered with litter, attracting rats and cockroaches.
It said there had been a "dramatic" increase in violence against staff, with more than 90 assaults in the six months to July, when inspectors visited the premises.
Chief Inspector of Prisons Peter Clarke said the findings painted an "extremely concerning picture".
The Ministry of Justice said the jail was recruiting staff in a bid to "urgently" raise standards.