Asmu's disappearance and death in the anti-communist Indonesian mass killings of 1965–66 following the September 30 Movement is poorly documented. Some newspapers later reported that he had been killed by the military in March 1966. Other sources claim he was killed in an extrajudicial killing in November 1965 and that his body was in an unmarked grave in the village of Kuntji Sidareja, northwest Cilacap Regency.