As get-rich-quick schemes go it was unusually complicated. Invade a foreign country you know little about. Abduct its president to the US. Collect a $15m bounty from the US government – and maybe an even bigger payoff from the people who then seize power.

The plan to overthrow Venezuela’s president, Nicolás Maduro, and bundle him off to Florida to face drug trafficking charges seemed foolproof to a former US army staff sergeant, Jordan Goudreau, as he mapped it out in a luxury Miami apartment in late 2019. The 43-year-old Canadian-American was certain his years as a green beret in Iraq and Afghanistan had prepared him for the task.

And for the opponents of Maduro he was addressing, it must have sounded convincing – even after the failure of a previous coup attempt in 2019.

Representatives of Juan Guaidó – the opposition leader recognised as Venezuela’s legitimate president by the US and most of its allies – signed a fat contract engaging Goudreau to overthrow Maduro.

But in interviews with the Guardian, a senior opposition figure said they grew to doubt Goudreau and eventually broke with him months before he launched this week a disastrous raid that echoed the botched 1961 Bay of Pigs invasion of Cuba.

The flaws in his plan were laid bare as two bedraggled ex-US special forces soldiers were paraded alongside other members of the ragged invasion force. Aaron Barry and Luke Denman were captured at sea before they even set foot on Venezuelan soil.

Eight people were reported killed in the botched invasion and more than 100 others arrested. Barry and Denman later appeared on Venezuelan state television outlining the supposed plan to seize the presidential palace and whisk Maduro to the US.

Goudreau announced what he called a “daring, amphibious raid” on Sunday afternoon. It was codenamed Operation Gideon after a biblical story symbolising the victory of a small military against a much stronger opponent.

“Our units have been activated in the south, west and in the east of Venezuela,” he said, dressed in a golf shirt and standing next to a former Venezuelan national guard captain wearing body armour, Javier Nieto Quintero.

But by then the plot had already fallen apart, not least because two days earlier the Associated Press had published a long investigation exposing the plan. If the AP knew it is likely the Venezuelan government did too.

Goudreau served in the Canadian military in the 1990s and studied at the University of Calgary before joining the US green berets. He spent 15 years as a medical sergeant, doing several stints in Iraq and Afghanistan.

After leaving the military Goudreau founded a security contractor, Silvercorp USA, in 2018. The company’s original plan was to provide guards to protect American schools from mass shootings.

Silvercorp’s website trumpets a series of overblown claims including that Goudreau led “international security teams for the President of the United States” (he had provided private security at Trump political rallies).

Early in 2019 Goudreau was providing security for a concert in aid of Venezuelan refugees on the Colombian border organised by Richard Branson, the billionaire owner of the Virgin conglomerate. There he met Cliver Alcalá, a Venezuelan former general who defected to the opposition. The pair began talking about how to overthrow Maduro.

By September the plotting had progressed to a meeting in Miami between Goudreau and Juan José Rendón, a Venezuelan exile appointed by Guaidó to strategise ways of taking power.

Rendón was well known in Latin American politics. He resigned as a strategist in then-Colombian president Juan Manuel Santos’s re-election campaigns amid allegations that he accepted bribes from drug lords. He was also accused of attempting to manipulate Mexico’s 2012 election. He has strongly denied both allegations.

Guaidó had set up an advisory group to brainstorm ways to end the Maduro regime. Rendón’s job was to advise the commission on how to make that happen.

He said the commission explored all legal means of ousting Maduro, including piracy laws. The commission also interviewed security consultants, mostly ex-soldiers offering specialist services for astronomical fees.

“There were no limits – $1bn, $1.5bn,” Rendón told the Guardian.

Goudreau’s firm was asking for far less – about $213m from Venezuela’s future oil earnings and a $1.5m retainer.

“He was supposedly preparing something in Venezuela that would have gone through the Colombian border,” Rendón said.

Goudreau told the Venezuelans he had 800 men ready to invade.

A handful of meetings resulted in an agreement in October for “an operation to capture/detain/remove Nicolás Maduro … remove the current regime and install the recognized Venezuelan President Juan Guaidó”.

Goudreau has made public pages from the agreement – one of them ostensibly signed by Guaidó. The would-be president has said that it is not his signature and has previously denied any involvement..

Rendón took the relationship seriously enough to pay Goudreau $50,000 of his own money to cover expenses. “He complained to me that I was a wealthy person and he was not and he was spending money,” Rendón said.

Under the agreement Silvercorp had 45 days to train and equip the invasion force before teams of men would infiltrate Venezuela to seize key locations and buildings, and encourage a general uprising.

But Rendón soon came to doubt that Goudreau had the military resources or competence he claimed, and grew concerned by his erratic behaviour – including his repeated demands for money.

Rendón showed the Guardian copies of increasingly angry texts he said were from Goudreau, demanding a $1.5m advance. “I will get the 1.5 the legal way. What a shame,” one text said. “We gave this to you on a silver platter and you fucked the whole thing up.”

“Your credibility in DC because of this is gone,” another text said. “You are a multimillionaire. Shame on you for not fixing your country. You don’t deserve to live in the USA.”

Neither Goudreau nor his lawyer returned calls seeking comment.

As the abortive raid was under way, Goudreau told Factores de Poder, a Miami-based Youtube channel: “They kept promising to pay week after week. So that lasted about a month but then we kind of realised that nothing was going to happen.”

Rendón said he lost confidence in Goudreau because of his “character, his moods” and “lack of respect”. He said Guaidó also began to suspect that Goudreau was talking too much.

“He was meeting with people in Colombia before meeting with us that were related to groups that we don’t engage with – because they are related to the regime,” said Rendón.

The dispute over the $1.5m retainer came to a head in a blazing row in November when Goudreau, Nieto and other exiles confronted Rendón at his Miami apartment.

“That conversation got heated, heated, heated and at the end Nieto intervened and we went to my balcony to chill,” Rendón said.

Goudreau left without his money. Rendón said he heard nothing more until April when he received a lawyer’s letter demanding payment of the $1.5m.

Rendón was not the first person to back away from a deal with Goudreau. Drew White, who served with Goudreau, Berry and Denman in the Middle East, helped set up Silvercorp. But he pulled out in 2019 when Goudreau started cooking up the plan to abduct Maduro, deciding it was too far fetched.

“As supportive as you want to be as a friend, his head wasn’t in the world of reality,” White told the Associated Press. “Nothing he said lined up.”

Ephraim Mattos, a former US navy Seal, who trained some of the would-be combatants in tactical medicine, told the Wall Street Journal he had tried to stop the operation.

Goudreau decided to press ahead anyway.

Preparations on the ground began to unravel in late March when Colombian police stopped Jorge Alberto Molinares driving along the Caribbean coast. His Renault Duster was packed with assault rifles, flak jackets and military helmets he was moving to a safe house in Riohacha, 55 miles from the Venezuelan border.

The authorities had begun watching the house after the landlord complained that the plotters had missed rent payments. Molinares told investigators he was delivering the shipment to a man known as to “El Pantera”, or the Panther, who Venezuelan authorities said was Robert Levin Colina Ibarra – subsequently killed in the botched invasion.

Goudreau’s plans were further complicated when his ally Alcalá, the former general, was indicted on the same drug trafficking charges as Maduro is facing. Before turning himself over to authorities Alcalá told the Guardian that he was working with the knowledge of “American contractors and the Colombian government” though he would not go into further details.

Unveiling the indictments in March, US authorities also offered a $15m reward for information leading to Maduro’s capture and prosecution.

With the big payoff agreed with Rendón dead, that made a potential payout from the US government all the more important for Goudreau. (The US secretary of state, Mike Pompeo, raised eyebrows this week by denying “direct” involvement in the plot.)

Berry, one of the captured American mercenaries, told state television that the plan was to abduct the president from his 19th-century official palace in the heart of Caracas, although he was uncertain how they wold carry that off. Denman told television that he was to secure a nearby military airport and bring in planes to carry Maduro out.

After the would-be liberators of Venezuela were herded ashore on Sunday, Maduro claimed that his agents had infiltrated the operation long ago and were ready to pounce. “We knew everything,” he said. “What they ate, what they didn’t eat. What they drank. Who financed them.”

Guaidó said that if the Venezuelan president let the operation go ahead in that knowledge, he had blood on his hands. “Nicolás Maduro you are responsible. They knew about the operation, they infiltrated them and waited for them to massacre them,” he said.

Goudreau sounded more sanguine even as Operation Gideon collapsed around him.

“I’m out a lot of money, a lot,” he said this week. “A lot of us came together to do this. I’ve been a freedom fighter my whole life. This is all I know.”