A man suspected over the killing of policewoman Sharon Beshenivsky was considered for deportation just months before the mother-of-three was shot.
Mustaf Jamma was not sent back to Somalia after serving his sentence
But the decision was taken not to send Mustaf Jamma back to war-torn Somalia because of the dangers he faced there.
Shadow home secretary David Davis said the case raised more questions in the row over foreign convicts' deportation.
Home Secretary Charles Clarke is due to update MPs on efforts to trace inmates who were freed and not deported.
Mr Davis said the fact that Mustaf Jamma is not one of those 1,023 people released from prison without deportation being considered just raised more questions.
"How safe are those decisions? How many of these people have been convicted of further crimes? How many are being investigated with respect to brutal crimes like the murder of Pc Sharon Beshenivsky?" he asked.
"Has the home secretary been monitoring this problem, since it clearly exposes another group of potential offenders who could put the public at risk?"
Local government minister David Miliband said the government had been unable to deport about 2,000 people.
"I think that's not because of some sort of squeamishness on the government's part, but we're dealing with countries which sometimes don't have governments or governments which simply won't co-operate with us in the deportation," he told the BBC's Newsnight.
Mr Miliband went on to reject claims that this latest twist in the foreign prisoners story made it harder for Mr Clarke to remain in his job.
"He's not going to run away from difficult problems; he's actually going to try and sort them out."
Mr Clarke is due in the Commons on Wednesday, shortly after Tony Blair's last Prime Minister's Questions before Thursday's local elections, to make a statement on the tracking of those criminals who were released and not deported.
Liberal Democrat home affairs spokesman Nick Clegg said: "This latest revelation underlines the invidious position the prime minister has put Charles Clarke in by refusing to accept his resignation.
"As long as Charles Clarke is prevented from assuming political responsibility for this chaotic state of affairs, he will continue to be buffeted by one allegation after another."
In a separate development on Tuesday, the Commons home affairs select committee said it would expand a current inquiry to include the foreign criminals debacle.
Mr Clarke and some of his Home Office officials will be called to give evidence later in the month.
The Press Association also reported that it had seen a 90-page circular setting out a strict timetable for considering foreign prisoner deportations sent on 31 March 2005 - meaning the Home Office was releasing prisoners for a year while those rules were in force.
The document, Prison Service Order 6000, describes a fail-safe system to deal with cases of foreign prisoners that had slipped through the net, with prisons told to identify whether inmates were liable to deportation as soon as they arrived at the jail.
Last week Mr Clarke said that 1,023 foreign criminals were freed without proper deportation consideration owing to a "failure in the system".
On Friday the home secretary said of the 79 most serious offenders - which included murderers and sex offenders, five had been convicted of more crimes since their release, and there had also been two allegations of rape.
Mr Blair meanwhile has urged voters to judge Labour on nine years in power not on the rows of the past few days involving Mr Clarke and John Prescott who had an affair with a secretary.
Responding to the home secretary's remarks that he should stay in his job to sort the problems out, Tory leader David Cameron said Mr Clarke had the chance to sort out the foreign prisoners issue nine months ago.
Pc Beshenivsky, 38, was shot dead and her colleague, Pc Teresa Milburn, was injured last November as they went to investigate reports of an armed robbery at a Bradford travel agents.