Police in Manchester are investigating the events leading up to the deaths of two inmates at the city's prison - formerly known as Strangeways.
The men were found dead in their shared cell at Manchester Prison
Shaun Hazelhurst, 28, and 32-year-old Patrick Kilty, were found hanged on Saturday morning in the cell they shared.
The men, both from Yorkshire, had been convicted of robbery and Hazelhurst was a week into a four-year sentence.
Greater Manchester Police are treating the deaths as suspicious.
They were found hanging from ligatures at 0700 BST.
Kilty was serving a life term and had been sentenced at Leeds Crown Court in December last year, while Hazelhurst had been sentenced at Manchester Crown Court on 27 August.
BBC correspondent Kevin Bocquet said the police were looking at two scenarios: a suicide pact between the two cellmates, or the possibility that one may have killed the other before taking his own life.
He said this incident brought the number of deaths by hanging at the jail to five in the last 12 months.
In a statement the Home Office said that Hazelhurst and Kilty had not been under special observation or suicide watch, and there did not appear to be any suspicious circumstances in relation to the deaths.
The men's relatives have been informed and post-mortems are due to be carried out shortly.
An investigation will be conducted by Prison Ombudsman Stephen Shaw, as in all cases of death in custody.
The deaths come just one day after a report revealed 14 prisoners had taken their lives in English jails in the month of August.
It was the highest figure for a single month since records began 20 years ago.
Commenting on the recent peak in the number of suicides in prison, Minister for Correctional Services Paul Goggins said: "The tragedy is for the individuals and their families.
"The paradox is that we have never done more to tackle self-harm and suicide in prison," he added.
"The number of people with mental health and other problems passing through our prisons is challenging for all concerned, but we cannot simply blame overcrowding: the prison population is lower now than it was six months ago.
"We will be working with the Department of Health to see what more we can do, and I have instructed the prison service to re-double their considerable efforts to prevent these tragic deaths."
An average of about 95 inmates take their lives in prison each year, out of a prison population in excess of 70,000.