A former city councilman from the party of presidential candidate Luiz Inacio Lula da Silva was shot and killed in Sao Paulo Friday, the party said, two days before the country's run-off presidential election.
The shooter's motivation was still under investigation, the party said.
"We received with much sadness and concern the news of the killing of our colleague Zezinho," Sao Paulo Worker's Party lawmaker Jilmar Tatto tweeted, saying the party would continue to closely watch "this crime and its motivations."
The shooting took place in Jandira, a municipality in the Sao Paulo metropolitan area.
News outlet G1 reported that police's "initial suspicion" is that the killing was motivated by "political revenge" related to complaints Zezinho planned to make about a suspected corruption scheme in the Jandira mayor's office.
Sao Paulo Security Secretary confirmed to AFP in a statement that "a man was killed via shots from a firearm Friday afternoon," and that officers were investigating, without offering further details.
According to local media, Zezinho, 51, had been a candidate in legislative polls that took place earlier this month alongside the first round presidential elections that saw leftist Lula and current right-wing President Jair Bolsonaro advance to the second round, set for Sunday.
He was currently working for the campaign of Fernando Haddad, who will appear on the ballot in Sunday's run-off elections as a candidate for governor in Sao Paulo.
Lawmaker Tatto told the O Globo newspaper that "everything indicates that it was an action by a Bolsonaro supporter within a climate of intolerance that is happening in the country."
In the two months leading up to the election's first round, Brazil has seen around two violent political episodes per day, according to NGOs Justica Global and Terra de Direitos.
A total of 121 cases of murders, attacks, threats or physical or verbal aggression were registered between August 1 and October 2.