BRASILIA, Brazil (AP) — A supporter of Brazil’s president used a knife and an axe to kill a backer of the main opposition leader after an argument about politics, weeks ahead of presidential elections, according to police.

The killing occurred on Wednesday, the day of Brazil’s independence bicentennial, near the town of Confresa, Mato Grosso state, in Brazil’s central-west region, a stronghold of President Jair Bolsonaro.

The 24-year-old suspect, who was not identified, killed Benedito Cardoso dos Santos, a 42-year-old farm worker who supports presidential candidate Luiz Inácio Lula da Silva, police said. Da Silva, a former president, is the main challenger to Bolsonaro ahead of a first round of voting on Oct. 2.

The two men in Mato Grosso worked together and got into a fight over the candidates they supported, according to the suspect’s account. He alleged that dos Santos attacked him first and tried to stab him.

In July, a Bolsonaro supporter allegedly shot and killed a local official of da Silva’s political party in the city of Foz do Iguaçu.