Stephen Fitzpatrick, Jayapura – Indonesian police have been driven by revenge and their own personal interests in a series of show trials over the deaths of four police and an air force sergeant in May (sic) riots, a new report claims.

The investigation, soon to be made public after months of documentation by a coalition of Papuan and national church and human rights groups, will allege that none of 23 men accused over the killings was directly involved in the deaths.

All but two of the accused have been sentenced to up to 15 years' jail, with the final pair of men appearing yesterday in Abepura District Court, near the Papuan capital, Jayapura.

The killings, at the peak of two days of demonstrations at Cendrawasih University over the giant Freeport McMoRan gold and copper mine in Timika, shocked Indonesians for their brutality.

The police victims were beaten with rocks and sticks after a crowd of students and other still-unidentified groups broke through a police line on March16.

Forensic investigations found that the air force sergeant, who was not in uniform, was killed in a separate knife attack on the university campus, Papua's largest.

However, as the final two of the 23 accused appeared yesterday in court, lawyers, church groups and supporters – as well as the men themselves - insisted their confessions were forced after beatings with rifle butts, pistols and fists, as well as electric shocks.

Mechanic Steven Wandik, accused of murdering air force sergeant Agung Prihadi Wijaya by smashing in his head with a large stone, said he was repeatedly beaten by police over a period of weeks before he offered a false confession to the crime.

He said he was taken from his home without warning in the middle of the night on May 12 – almost two months after the riots – and forced into a police vehicle after being hit in the head with a rifle butt. He said he was too frightened to offer resistance, and that for several weeks police offered no explanation for his arrest.

Wandik says his name was given to police by a cousin, Sam Wandik – the other man on trial in Abepura District Court yesterday. Sam Wandik told the court he provided his cousin's name as someone involved in the killings only after repeated beatings and electric shocks.

Asked after his appearance yesterday why he was now recanting on his allegation, Sam Wandik said: "Because I'm being held in the jail now, not in the police cells, and the police can't hurt me there."

Aloy Renuarin, the Papua head of Indonesian human rights group ELSHAM, later described the 23 men as "victims of police revenge" and said the convictions had so far been based on "incredibly weak evidence". "This is a matter of politics, of a legal mafia and of the courts and government discriminating against Papuans," Mr Renuarin said.

Appeals were lodged yesterday in five of the cases.

Evidence given in Steven Wandik's prosecution has included photographs of the accused participating in a police reconstruction of the crime.