The leader of a landless peasant movement in Paraguay involved in a land dispute with a powerful politician has been shot dead.
Vidal Vega had been co-operating with an inquiry into the deaths of 11 of his supporters and six police officers.
They died last June in an operation to evict farmers from land which activists say was illegally grabbed by a late senator in the 1960s.
Then-President Fernando Lugo was ousted over his handling of the deadly clash.
A prosecutor investigating his murder said two gunmen arrived at his home in Curuguaty in the eastern province of Canindeyu and shot him early on Sunday.
The prosecutor said police had later arrested a suspect who matched the description of one of the gunmen, but did not speculate on a motive.
He said there was no evidence so far linking Mr Vega's murder to his role in the investigation into the killings in June.
Mr Vega, 48, was expected to testify at the trial.
His movement of landless peasants had lobbied the Paraguayan government for many years to redistribute farmland in Canindeyu occupied by late senator Blas Riquelme more than 50 years ago.
They say the land was illegally taken during the military rule of Gen Alfredo Stroessner and distributed among his allies.