Dorothy Stang had spent decades defending Para's peasant settlers

Vitalmiro Moura - who turned himself in accompanied by a lawyer - denied involvement in the 12 February attack.

Three other suspects are being questioned on the murder which police believe was a contract killing.

Dorothy Stang, 74, had campaigned for more than 30 years for the rights of peasant farmers in the Amazon.

Following the killing in the northern state of Para, the Brazilian government sent in thousands of troops to try to restore order to the lawless jungle region.

Revolver found

Mr Moura surrendered in the city in the city of Altamira, about 130km (80 miles) from the place near Anapu where the nun was gunned down.

He was taken into custody after his lawyer negotiated with police to guarantee his safety.

Mr Moura is due to be interrogated in the next few days, police say.

Officials have earlier said a revolver found on Mr Moura's farm was connected by ballistic tests to the bullets recovered from the missionary's body.

After the murder, the government said it planned to protect a huge swathe of the Amazon.

It said nearly four million hectares (10 million acres) in Para state would become a conservation area in a bid to ward off loggers and landowners.

The government said it also wanted to reinforce the environmental police force.