A court in Peru acquitted on Thursday 52 Amazon natives for the murder of 12 police officers seven years ago during protests against laws that indigenous groups said facilitated the usurpation of their lands for oil and timber development.

The court in Bagua also struck down charges of rebellion and causing serious injury presented by prosecutors during the years-long trial.

Officials said the people of accused of shooting the officers during the protests tested negative for gunfire residue. Judge Gonzalo Zabarburu said the true killers have still not been identified.

The confrontation, in which hundreds of police tried to dislodge members of local indigenous tribes blocking a highway, occurred at a remote area called the Devil's Curve, where the Andean foothills meet the Amazon jungle. It is not far from the city of Bagua.

Ahead of the June 5, 2009 clash, thousands of spear-toting natives, some with faces daubed in war paint, had massed to defend the rainforest against legislative decrees they saw as part of a land grab by multinationals under a free-trade deals.

Ten civilians died in the clash in addition to the 12 police.

Hours later, several miles away, another clash left more police officers dead.

Soon after the killings, Peru's Congress overturned the two disputed decrees. One of the decrees allowed investment in the Amazon with authorization from Lima without any consultations with the tribes affected.

Amazon Watch welcomed the acquittal of the indigenous leaders but called the process a prolonged injustice.

"The real perpetrators of the Bagua massacre — political actors and economic interests — enjoy total impunity to date," the group said in a statement.