The former prison chief whose trial by Cambodia’s genocide tribunal is coming to an end was a willing, even enthusiastic, participant in atrocities committed by the Khmer Rouge, prosecutors charged Tuesday.

The prosecution, making its closing arguments, is demanding a lengthy prison term for Kaing Guek Eav, who commanded S-21 prison when the communist group held power in 1975-79, and oversaw the torture and execution there of about 16,000 men, women and children accused of disloyalty.