Papua New Guinea's prime minister, Peter O'Neill, wants police to reopen a case into the torching of an Air Niugini plane last year.
In June, the plane and government buildings in the Southern Highlands capital were burnt, triggering a state of emergency in the province.
The unrest followed a court decision upholding the 2017 election win of Southern Highlands governor William Powi.
She said there was not enough evidence to commit the men to trial in the National Court.
Police in Mendi had failed to conduct an identification parade to pick out the offenders, the judge said.
They had also failed to help detectives from other centres to properly investigate the matter.
However, the National newspaper reported Mr O'Neill saying there was enough video evidence in circulation.
Such behaviour could not go unpunished and the case would be reopened, Mr O'Neill said.
Police Minister Jelta Wong said he had already directed Police Commissioner Gari Baki to look into the matter.