Jair Bolsonaro had just nine weeks to pull off a plan that was both risky and extraordinary. With the help of allies, prosecutors say, he was intent on overturning the October 2022 presidential election he had lost.

A close aide came up with a sinister solution: poisoning Luiz Inácio Lula da Silva, who had defeated Mr. Bolsonaro, before he was sworn in as Brazil’s next president on New Year’s Day 2023, according to a document that had been printed at the presidential offices while Mr. Bolsonaro was in the building.

“Lula does not walk up the ramp,” referring to the sloped path to the presidential offices, said another document seized during a police raid on Mr. Bolsonaro’s party headquarters.

Mr. Bolsonaro, who denies plotting to kill Mr. Lula, will stand trial on Tuesday before Brazil’s Supreme Court on charges that he oversaw a sweeping plan to cling to power in a case many see as a crucial test of the country’s young democracy. With a vast trove of prosecutorial evidence, most analysts say he is almost certain to be found guilty and could face decades in prison.

To piece together the case against Mr. Bolsonaro, The New York Times reviewed dozens of hours of testimony and hundreds of pages of police and prosecution documents from an investigation spanning nearly two years.

Prosecutors and Mr. Bolsonaro’s defense each point to the evidence to tell sharply diverging stories.