(Times of India ) – Thirteen people, including the head of a local prison, have been arrested over last weekends twin bombings in a Christian town that killed 20 people, the national police chief said on Wednesday. None have been formally charged over the blasts at a bustling market in Tentena on Sulawesi Island , which authorities initially blamed on a gang of Islamic extremists responsible for other attacks in the region in recent years. Under the countrys tough, anti-terror law, police can hold suspects for seven days without charging them. “We have arrested 13 suspects and we have strong indications that they are the perpetrators in the Tentena bombing, National Police Chief General Dai Bachtiar said. “Police are still searching for two other suspects. The two were executors in the field and have been involved in several acts of violence in Maluku province.” One of the men being questioned is the chief warden of the jail in Poso, a mostly Muslim town close to Tentena, national police spokesman Soenarko Danuarwanto said earlier.