Unidentified gunmen forced their way into an Indonesian jail early on Saturday and shot dead four prisoners awaiting trial over the death of a soldier, police said.
Armed police stand guard after a shooting inside the Cebongan Correctional Centre in Yogyakarta on Saturday.
The prisoners were accused of beating and stabbing to death a soldier from the elite Special Forces Command on Tuesday at a nightclub in Yogyakarta in central Java as he reportedly tried to break up a fight.
National police spokesman Suhardi Alius said around 15 gunmen entered the Cebongan Correctional Centre after intimidating and then beating two guards at around 1 am.
"At one o'clock, masked men carrying guns got into the prison and found the four men. They shot them in their cell and left immediately," Alius told reporters, adding that one of the four prisoners was a former police officer.
He said 15 people, including guards and prisoners, were being questioned as witnesses and that police had recovered bullets and shells.
Alius declined to confirm whether police were seeking members of the Special Forces.
Yogyakarta police spokeswoman Anny Pudjiastuti said the four bodies had been taken to hospital for autopsy.
She said police were trying to study CCTV footage, but another police source close to the case said the gunmen had deliberately destroyed some of the cameras.
The source said the gunmen were armed with AK-47 assault rifles and at least one pistol, and that they had threatened to knock down the prison door with grenades.
In Indonesia, suspects in serious cases are often held in police cells with no bail option after arrest and before being formally charged in court.
The four men, and seven others, were being held in the correctional centre as the regional police station was undergoing renovations.