An investigation into a house burning campaign during the 1980s is being reopened by North Wales Police.
Meibion Glyndwr targeted holiday homes in a campaign of arson
The so-called Meibion Glyndwr - Sons of Glyndwr - attacked over 200 hundred homes, caravans and cars in Wales, in protest against rural homes being sold as holiday cottages to people from England.
Detectives hope advances in technology - especially DNA techniques - will help them in the quest to catch the group which has eluded them since 1979.
The force's deputy chief constable Clive Wolfendale told the BBC Wales current affairs programme Taro Naw that material kept over its 14-year inquiry will be examined to find whether it will yield DNA evidence.
The MP for Clwyd West and solicitor Gareth Thomas said he was "mystified" as to why the force had now decided to re-open the investigation.
"The DNA technology there'll be using has existed for at least five years," he said.
"It's a reasonable requirement that police review old cases but I'm mystified as to why it's been decided now."
Mr Wolfendale's announcement came after the former head of North Wales CID told Taro Naw, broadcast on Tuesday evening, that some officers in the force - but who were outside the unit investigating the arsonists - supported the actions of the group.
But one commentator has said the decision to reopen the inquiry could prove controversial.
Sion Aubrey Roberts - jailed for sending letter bombs
Historian Dr John Davies said the widespread sympathy for the campaign in certain areas of Wales was such that fresh arrests from a new police investigation could lead to the start of a similar campaign.
Meibion Glyndwr began burning property in December 1979 in protest at what it claimed was a growing trend of homes in rural Wales being sold as holiday cottages to people from England.
Properties were attacked during a campaign lasting until the mid-1990s.
Police were accused in some quarters of targeting anyone who was a nationalist and although one man, Sion Aubrey Roberts, was convicted in 1993 of sending letter bombs in the post, the cases remain unsolved.
Mr Wolfendale said on Tuesday: "We have a policy of going back and looking at serious crimes and we have started to reinvestigate the campaign to burn cottages.
But retired detective Gareth Jones, who led the north Wales force's CID, said: "There's no doubt that some police outside this unit were supportive of what was going on.
"I have no doubt about that and we had to co-operate and work with those people, but nobody was open about it at the time of course."
Meibion Glyndwr - named after 15th Century rebel leader Owain Glyndwr - said in 1989 that "every white settler" was a target for their campaign.