The killing came hours after a delay in the trial of a man accused of masterminding the slaying of another rain forest activist, American nun Dorothy Stang, who was shot and killed in 2005 in notoriously violent Para state.

Watchdog groups say conflicts between powerful ranchers and poor farmers over land rights have led to 1,200 murders across Brazil in the last 20 years.

In only one of those killings – Stang's – is the alleged mastermind now behind bars. About 80 of the gunmen are in jail.

Pedro Alcantara de Souza, who headed a union of landless farmers in Para, was shot in the head five times by two men on motorcycles, according to a police spokesman in the town of Redencao.

Souza was riding a bicycle on the outskirts of the town and his wife was with him when he was shot, the spokesman said. He added police were working on the assumption Souza was killed because of his political activities.

The official spoke on condition of anonymity as he was not authorized to discuss the case.

The gunmen are not in custody, but state officials are sending a special team of investigators from the capital Belem to the area, about 750 kilometers (465 miles) to the south, the spokesman added.

Souza was a city councilman for 14 years before stepping down in 1996. As the head of a union of landless farmers, he led occupations of massive farms that had land they argue is unproductive.

Brazil's agrarian reforms laws state that unused farmland can be taken by the government and distributed among landless farmers.

Though there have been improvements in recent years, severe economic inequality persists in Brazil – and that includes land ownership. The Brazilian government's statistics agency says nearly 50 percent of arable land belongs to just 1 percent of the population.

Stang, a Dayton, Ohio, native, promoted the land rights of poor farmers for three decades. Prosecutors allege she was murdered on orders from two powerful ranchers because she blocked them from illegally obtaining property that the government handed over to a group of small farmers.

Activists and state officials worry that the killing of land reform and jungle-protection leaders frightens the rank-and-file members of the movements, weakening them.

"If we cannot convict those who kill these leaders, then we cannot maintain the fight to preserve the forest," said Edson Souza, the prosecutor in the Stang case.

Rancher Vitalmiro Moura is accused of ordering Stang's murder and faces his third trial in the case. He was convicted once, then found innocent, though that was overturned on a technicality last year.

His latest trial was to scheduled to begin Wednesday. But a state judge ordered it delayed until April 12 on a request from the defense.

Huffington Post