Asuncion, Paraguay (CNN) -- A well-known candidate for Paraguay's presidency died in a helicopter crash while on the campaign trail, authorities said Sunday.
Retired Gen. Lino Cesar Oviedo died late Saturday night when the helicopter he was traveling in plunged to the ground in western Paraguay, officials said. He was 69.
Investigators found the charred helicopter wreckage Sunday morning and discovered that Oviedo, his bodyguard and the chopper's pilot had perished, Paraguay's civil aviation authority said.
While authorities said it was unclear what caused the crash, some supporters of Oviedo said the circumstances were suspicious.
Oviedo's sudden death in the heart of campaign season sent shock waves across Paraguay's political landscape less than three months before the presidential vote.
"We will hire international experts in aerial accidents to investigate what happened in a clear and objective manner," Paraguayan President Federico Franco said in a written statement.
Franco declared three days of national mourning in honor of Oviedo, describing him as a "military hero" and praising his role in the February 3, 1989, coup that ended military dictator Gen. Alfredo Stroessner's 35-year rule.
In a Twitter post, the National Union of Ethical Citizens political party he founded described him as "the father of democracy."
Oviedo was a controversial figure in Paraguay, beloved by his supporters and despised by enemies, some of whom accused him of trying to undemocratically seize power in the country.
Oviedo first ran for president in 1998, but he was taken out of the running after a military tribunal sentenced him to 10 years in prison for his role in a 1996 coup attempt.
A 2007 Paraguayan Supreme Court ruling overturned his sentence. Shortly afterward, he hit the campaign trail again, signing up to run in Paraguay's 2008 presidential election.
In that election, he finished third, garnering 21% of votes.
But that didn't stop him from signing up to run again this year.
"If they don't kill me, I am going to win the 2013 elections," Oviedo told Paraguay's La Nacion newspaper in 2011.
The announcement of his death on the 24-year annivesary of the 1989 coup that he helped lead sparked suspicion among one of his top allies.
"It's too much of a coincidence," said Cesar Durand, a spokesman for Oviedo's party, in an interview with Paraguay's Radio Cardinal.
"We are not going to permit this to go unpunished. ... I have absolutely no doubt that this is a political crime," he said.
Paraguay's Senate president described the circumstances of the accident as "strange," but said the party would accept the results of the official investigation, the government-run IP Paraguay news agency reported.
Journalist Sanie Lopez reported from Asuncion, Paraguay. CNN's Catherine E. Shoichet reported from Atlanta.