The deaths were shortly before the 1969 investiture at Caernarfon Castle
A peer is calling for an inquiry into a bombing before the Prince of Wales' investiture more than 40 years ago.
It has always been assumed that both Alwyn Jones and George Taylor planted the bomb which ended up killing them both in Abergele, Conwy county.
Lord Roberts of Llandudno says National Archives documents suggest a different interpretation of Mr Taylor's role.
The Lib Dem peer told BBC Radio Cymru's Manylu programme there was already enough evidence to justify an inquiry.
Lord Roberts has taken what he hopes will be the first step by writing to Security Minister Lord West.
The programme has also heard from a former member of Special Branch who worked on the investigation after the explosion.
The ceremony went ahead as planned on 1 July 1969, when the 20-year-old Prince Charles was invested as Prince of Wales by the Queen at Caernarfon Castle.
The former Special Branch man told Manylu that one of the men killed at Abergele was already suspected of being invoved in at least one bombing incident, but that Mr Taylor was not on their radar.
Press reports in 1969 said the two men who were killed had set off with the "apparent intention" of placing the bomb near the route of the train carrying members of the Royal Family.
'No threat to prince'
John Jenkins, a former leader of Mudiad Amddiffyn Cymru (Movement for the Defence of Wales), has since said that the pair did not intend to bomb the royal train.
Mr Jenkins, who was jailed for 10 years in 1970 after pleading guilty to eight charges relating to explosives and conspiracy, told the Western Mail: "I've made it clear all along that there was no threat to the prince at all.
"Our priorities were about hearts and minds and awakening national consciousness and this would hardly have been helped by targeting people at any stage."
A verdict of accidental death was recorded at the inquest in October 1969 on the two men.
The deaths have continued to prove controversial, and there was a row last year on the 40th anniversary when a march was promoted on Facebook to commemorate the deaths.
The Facebook posting said the group organising the event "does not promote violence" but "debate about Welsh history and politics," and stressed that "under no circumstances are we calling for the actions of these men to be repeated".
But some Conservative politicians criticised the staging of the march - which was attended by about 80 people - and the fact that North Wales Police had offered to police it.
At the time the force said they had a duty to police such events "in a proportionate, lawful and impartial manner".
Manylu is on BBC Radio Cymru just after 1800GMT on Monday, 22 March.