Police have charged five more suspects in a spate of deadly shootings at the Indonesian gold mine of US company Freeport, but the motive for the attacks remains a mystery, officials said Friday.

In a doorstop interview following Friday prayers, National Police Headquarters spokesman Nanan Sukarna said that police had now apprehended five additional suspects.

Police had already apprehended seven people believed to be involved with the attacks. They are accused of premeditated murder and illegal weapons possession for the series of ambushes that left three dead earlier this month at the Grasberg complex in Papua, the largest gold mine in the world. Among those charged are two Freeport employees, but their role is still unclear.

A 29-year-old Australian worker and a Freeport guard were shot to death during the attacks and a police officer fell to his death seeking cover from gunfire.

It is the worst violence at the site since three schoolteachers, two of them Americans, were killed in 2002.

Papua police chief Bagus Ekodanto said Friday it is still unclear if the culprits are members of the Free Papua Movement, which has waged a low-level insurgency against the government for 40 years, or a different armed group.

Freeport has been targeted with arson, roadside bombs and blockades since production began in the 1970s during the US-backed Suharto dictatorship. It is also regularly the focus of protests by local residents who feel they are not benefiting from Papua's natural resources. (JG, AP)