Larkin said very few paramilitary figures had been convicted of pre-1998 crimes over the past 15 years. "Every competent criminal lawyer will tell you the prospects of conviction diminish, perhaps exponentially, with each passing year," he said.
"It strikes me that the time has come to think about putting a line, set at Good Friday 1998, with respect to prosecutions, inquests and other inquiries," he said.
His views drew criticism from politicians on both sides.
"This proposal would deprive innocent victims of the right to justice," said Nigel Dodds, deputy leader of the major Protestant-backed party, the Democratic Unionists. "The pain, for many victims, is still as raw today as it was when they first were injured or learned of their loss."
Any amnesty on prosecuting people for Northern Ireland-related attacks would require legislation in both the United Kingdom, which includes Northern Ireland, and the Republic of Ireland. The conflict's death toll includes more than 120 people killed in England, chiefly in IRA bomb attacks, and 100 killed in the Irish Republic.
British Prime Minister David Cameron dismissed Larkin's idea as legally dangerous.
"We are all democrats who believe in the rule of law, who believe in the independence of the police and prosecuting authorities," Cameron told lawmakers in the House of Commons in London. "They should, if they are able to, be able to bring cases. I think it's rather dangerous to think that you can put some sort of block on that."
But Northern Ireland's police commander, Chief Constable Matt Baggott, said pursuing pre-1998 slayings probes tied up too many staff and too much money, weakening his force's ability to investigate more recent crimes. His force runs a cold cases unit called the Historical Enquiries Team and is separately investigating the killing of 13 unarmed Catholic demonstrators by British soldiers on Bloody Sunday in 1972.
"It is well documented that the cost of policing the past has a massive impact on how we deal with the present and the future," Baggott said.
A former Cabinet minister responsible for Northern Ireland affairs in Britain's previous government, Peter Hain, called Larkin's views "common sense."
Hain said it would be better for the government to invest in benefits and supports for victims' families than to "pursue crimes committed three or four decades ago at enormous expense, with enormous effort, where the evidence is very difficult if not impossible to achieve."
Larkin made his position public after presenting his proposals formally to Richard Haass, a former top U.S. State Department official.
Haass, who was President George W. Bush's envoy to Northern Ireland, is back in Belfast at the request of the Northern Ireland government to develop proposals for addressing unresolved disputes between the province's British Protestant majority and Irish Catholic minority. He is expected to deliver his report to the government next month.
