The Khmer Rouge tribunal will not investigate allegations of forced pregnancy during the Democratic Kampuchea regime in its Case 004, citing issues of legality, timing and a lack of evidence in a decision made public on Wednesday evening.

Civil party lawyers and the prosecution had launched separate but similar requests to investigate forced impregnation in the case against suspects Ao An and Yim Tith. Both requests, however, were denied by the office of the co-investigating judges, who said in a decision that forced pregnancy was not defined as a distinct crime between 1975 and 1979.

It was not until the Rome Statue of the International Criminal Court in 1998 that it was legally recognised.

The decision said that, furthermore: “There is at present, after years of investigation into forced marriage, no evidence that would support a policy of forced impregnation or forced pregnancy.

“Both requests were filed very late in the day without good cause having been shown; extending the investigation now would put an undue burden on the Defence and cause an unacceptable delay in the investigations.”

But civil party lawyer Linda Behnke, who applied for forced pregnancy to be examined as a distinct – and inherently gendered – crime, said she was “disappointed”, and that the court had missed an opportunity to investigate the crime.

“We know the practice of forced marriage was very common; it’s something that many of our clients experienced,” she said. “They were being coerced to consummate the marriage – often, there were people spying on them and they would pay some kind of punishment [if they didn’t].”

Witnesses in the current trial have testified that couples were closely monitored, and those who did not consummate were reported to the upper echelons for their so-called betrayal.

Behnke said pregnancies were more difficult to bear due to limited health care, being forced to work straight after birth and breastfeeding problems stemming from harsh living conditions.

Those experiences, coupled with Khmer Rouge documents that endorse a policy of population growth, compelled the lawyers representing victims to file a request with the investigating judges.

According to a March 2016 report into forced marriage under the Khmer Rouge, authored by Maria Lobato and published by the Cambodian Human Rights Action Coalition (CHRAC), no international or hybrid criminal tribunal has ever prosecuted the crime of forced pregnancy.