The Prosecutor General's Office in Venezuela named three men, aged between 22 and 28, who it said were arrested Monday in the town of Altagracia de Orituco.
"The three men will be accused for their presumed link to Luis Manuel Diaz's death," the office said, without giving further details.
Opposition leaders blamed last week's shooting of Diaz, 44, a parliamentary candidate for the Democratic Action party in central Guarico state, on the ruling Socialists.
But President Nicolas Maduro's government denied the accusations. Officials say Diaz was a well-known criminal caught in a gang dispute linked to unions in Guarico, and his death was being manipulated to discredit the Socialist Party.
The murder of Diaz has heightened Venezuelans' fears of volatility around Sunday's vote for a new National Assembly. Currently polls show the opposition could win for the first time in 16 years.
Venezuela's opposition also sent a message to the armed forces on Monday, urging them to respect Sunday's results and not to block any potential change of power in the National Assembly.
Venezuela's economic crisis, which includes the world's highest inflation and widespread shortages from eggs to electronics, has hurt the popularity of Maduro, who won election in 2013 after the death of his far more popular predecessor Hugo Chavez.
Even though various polls show the opposition Democratic Unity coalition ahead on nationwide voting tendencies and anti-Maduro leaders are confident, the ruling party has advantages due to the split up of electoral districts as well as superior campaign resources.
One pollster, Luis-Vicente Leon, said that even though Maduro's popularity had improved in recent days, thanks to the government's strident campaign, the opposition was still the favorite. "The question is how big a majority they achieve," he said.
av/gsw (AP; Reuters)