Nine Tanzanians have been charged in connection with the murder of a British conservationist whose helicopter was shot down while he chased suspected poachers, a senior prosecutor has said.

Roger Gower, 37, died when suspected poachers gunned down his helicopter during a patrol of the Maswa game reserve in northern Tanzania, close to the Serengeti national park, on 29 January.

Photographs of the crashed helicopter show twisted metal, apparent bullet holes in the fuselage and smears of blood on the pilot’s seat.

“Four of them are charged with murder, while others face charges of economic sabotage and unlawful possession of firearms,” senior government prosecutor Yamiko Mlekana told AFP by phone on Thursday.

The four men charged with murder have not yet entered any plea, as their case will be tried in the high court. The other five will be tried in a lower court.

“Some of the accused pleaded guilty to being in unlawful possession of firearms and elephant tusks, while others denied the charge,” Mlekana said.

Gower, who worked for the Friedkin Conservation Fund, had been tracking poachers after spotting the carcasses of recently killed elephants.

It is estimated that more than 30,000 elephants are killed for their tusks every year across Africa.

Their ivory is prized for jewellery and decorative objects and much of it is smuggled to China, where many increasingly wealthy shoppers are buying ivory trinkets as a sign of financial success.

Tanzania’s natural resources and tourism minister, Jumanne Maghembe, this week announced the government would set up a special task force for anti-poaching operations.

“Poaching is now done using sophisticated machinery and heavy weapons including AK-47s,” Maghembe said. “We are going to set up a force comprising different security forces and the army.”