Wildlife conservationist Wayne Lotter was shot dead in the Tanzanian city of Dar es Salaam, The Guardian reported on Friday. He was being driven from the airport to his hotel when an armed man killed him on Wednesday.

Lotter, a South African, had received many death threats over the years. He was the co-founder of the Protected Area Management System foundation, which worked on protecting wildlife and raising awareness. He had worked on many high-profile Ivory smuggling cases that led to many arrests.

The murder is being investigated by Tanzanian authorities. The motive for the killing is unclear though the involvement of ivory poachers is suspected. His laptop was also stolen in the attack, Reuters reported.

“His ground-breaking work in developing an intelligence-based approach to anti-poaching helped successfully reverse the rampant rates of poaching facing Tanzania,” a statement by his foundation said. “He died bravely fighting for the cause he was most passionate about.