The Khmer Rouge tribunal’s international co-prosecutor said he will appeal the investigating judges’ decision to dismiss the case against Im Chaem on the grounds that she was not a senior leader and could not be tried as one of those “most responsible” for the crimes under the regime.

The judges said the former Preah Netr Preah district secretary “had the authority to order executions” and was a “trusted and close aide” of Ta Mok, known as “the butcher”, who purged Khmer Rouge soldiers. Yet ultimately – in a document that was largely censored – they deemed Chaem too lowly in the Khmer Rouge leadership to face the court.

In a document made public on Friday, International Co-Prosecutor Nicholas Koumjian notified the tribunal that he intended to appeal that decision. However, the co-prosecutor declined to comment on the appeal, saying the matter was “covered by orders of confidentiality”.

Koumjian’s move goes against the grain of not only the investigating judges but also his Cambodian counterpart. Since December last year, National Co-Prosecutor Chea Leang has argued that Chaem fell outside the jurisdiction of the tribunal.

Chaem’s defence lawyer, Bit Seanglim, declined to comment, but her legal team in a statement last week urged Koumjian to “appropriately consider and weigh the interests of justice and of Ms. Im Chaem in deciding whether or not to pursue an appeal”.

“[A]n appeal is unlikely to respect the boundaries of the law and would weigh heavily against the interests of justice as a whole, including our client’s right to a fair and expeditious trial.”