The Lumajang Police in East Java have arrested 36 people on suspicion of involvement in a deadly assault that claimed the life of a local farmer who had co-arranged a protest against invasive sand-mining in his village. Lumajang Police's criminal investigation unit chief Adj. Comr. Heri Sugiono said his office, however, had yet to formally name any suspects, as the investigation was still ongoing. "We are still conducting field checks, going deeper into the case. We are also still questioning a number of witnesses," Heri said on Saturday as quoted by tribunnews.com. Earlier on Saturday, a 52-year-old villager named Salim, or Kancil, was allegedly beaten to death by a group of people in Selok Awar-Awar subdistrict, Pasirian district. The same group also allegedly assaulted Tosan, 51, another villager, leaving him in a critical condition. Three days before the incident, the two victims, along with dozens of fellow villagers, staged a rally to protest against sand-quarrying activities on Watu Pecak Beach, also in Selok Awar-Awar subdistrict. The protesters claimed that the mining damaged the environment, leaving holes 5 meters in diameter and a meter deep on the beach. The protest halted the quarrying and blocked dozens of trucks transporting the sand. Heri confirmed that Salim and Tosan had both fallen victim to collective assault. "For now, the case involves an investigation into collective assault," he said. Shortly after the incident, the police arrested two men, identified as Dasir and Siari, whom several witnesses pointed to as the main perpetrators of the assault. Ten others later turned themselves into the police. As of Sunday morning, 36 people were in police custody. Lumajang, a home to 1 million people, is located some 150 kilometers southeast of the East Java provincial capital of Surabaya. Indonesian Forum for the Environment (Walhi) East Java chapter director Ony Mahardika said the incident indicated the vested interests of the companies involved in sand-mining in the area. According to Walhi data, 13 companies have been granted sand- and gravel-mining concessions from state-owned forestry firm Perhutani, which owns the land. According to Ony, each of the 13 companies holds a concession with an average area of 5,000 hectares. The site where the villagers staged their rally belongs to PT Indo Multi Mineral Sejahtera, which holds a concession to operate mining activities on a 4,000 ha plot of land. Ony condemned the deadly assault and urged law enforcers to investigate the case. "I have been assured that a member of the presidential staff will visit the crime scene soon," he told The Jakarta Post on Sunday. According to Walhi data, Salim's death is the first case of an environmental activist being murdered in East Java. However, Ony added, the incident could have been predicted and prevented, as intimidation tactics against antimining protesters had long been used in the province, and reports of such tactics had been filed to both the provincial and national government.