By Steve Kingstone
BBC News, Sao Paulo
Police in Brazil have arrested three men on suspicion of murder, following a violent confrontation over land rights.
Landless workers' occupation of land has caused conflict
Five people were killed on Saturday when gunmen opened fire on a settlement on occupied farmland in the state of Minas Gerais.
The victims were members of Brazil's Landless Workers' Movement (MST) that had occupied the site in 2002.
The police now want to speak to a local landowner who is suspected of ordering the killing.
In a country where nearly half the farmland is owned by just 1% of the population, conflict is perhaps inevitable. But these killings have nonetheless shocked Brazil.
In a statement, the governing Workers' Party called the murders cowardly and brutal.
Visiting the scene of the attack on Sunday, the country's human rights minister said these were premeditated crimes which would not go unpunished.
The attackers struck on Saturday afternoon, firing shots at the makeshift settlement on farmland near the town of Felizburgo.
The victims, all MST members, had moved onto the site two years ago.
They say the land belongs to the state and had fallen into disuse, but it seems that brought them into conflict with the local farmer who claimed the site for himself. The police want to speak to him.
For the Brazilian government, this is a timely reminder of the explosiveness of this issue. The number of deaths in confrontations over land has increased during the presidency of Luiz Inacio Lula da Silva.
As a long-standing friend of the MST, he promised to resettle more than 100,000 families this year.
But with funding tight, he is well behind that target, which is why many activists take matters into their own hands, occupying disused land and risking confrontation with farmers.