Investigating judges at the Khmer Rouge tribunal are set to tackle a legal question that has never been asked: whether an attack by the state on its own army counts as an attack on their civilians and, consequently, a crime against humanity.

International co-investigating judge Michael Bohlander called for experts and defence teams to weigh in on the issue for Case 003, brought against the alleged former Khmer Rouge navy commander Meas Muth, but the outcome could potentially impact Case 004 as well.

In late April, judge Bohlander wrote that armed forces do not qualify as civilians before the Extraordinary Chambers in the Court of Cambodia (ECCC), but this has only been articulated in terms of a foreign or enemy army – not the state’s own combatants.

The line between army and civilian blurred when the Khmer Rouge allegedly purged its own cadre, which, Bohlander signals, could equate to a crime against humanity committed against civilians.

Muth’s international defender Michael Karnavas welcomed the move, saying the complex issue had not yet been addressed by other international courts for the 1975-1979 timeframe.

“It is refreshing that the defense is asked to weigh in on the issue, though I think we need to be guarded against reading too much into this gesture,” he said via email.

“The real issue as far as I am concerned is whether the ECCC has the intellectual honesty and courage to apply the then-existing law which may give rise to inconvenient or unsatisfying results.”

He said a solution would involve examining the past laws as they stood, because the court “cannot simply look at where the law is today” or “legislate from the bench” in line with judges’ personal legal theories.

Khmer Rouge tribunal monitor Heather Ryan, of the Open Society Justice Initiative, said the step indicated “an inclination to rule that an attack by state forces against one’s own military members does constitute an attack against a civilian population for purposes of constituting a crime against humanity”.

The fact that the tribunal may be the first to broach the issue “evidences the unusual nature of the Khmer Rouge crimes against Cambodian people”, she said.

“In retrospect the question raised seems very basic and it is surprising that it has not been raised and resolved previously . . . but such questions are sometimes avoided for strategic reasons.”

Judge Bohlander declined to respond to questions, citing the confidentiality of the investigation.