O N THE NIGHT of November 8th, Jorge Enrique Pizano’s wife found him lying on the bathroom floor in their house north of Bogotá, the capital, wrapped in a towel and breathing heavily. He died on his way to hospital. The cause was a heart attack, said forensic experts. Three days later, his son, Alejandro, who had returned from Spain for his father’s funeral, took a sip from a water bottle on Mr Pizano’s desk. He complained of a foul taste, fainted and died moments later. Doctors said he had been poisoned with cyanide. His stomach, they said, was destroyed by the toxin. Alejandro’s apparent poisoning raises questions about whether his father was the victim of foul play, too.

The death of the Pizanos is the most dramatic twist yet in Colombia’s biggest corruption scandal. The case involves Odebrecht, a Brazilian construction firm that has bribed officials in a dozen Latin American countries, and Grupo Aval, Colombia’s biggest financial group. The two firms were partners in a $1.6bn contract to build Ruta del Sol, a motorway linking the capital region and the Caribbean coast.

Documents and recordings made public show that Mr Pizano, an auditor for Grupo Aval, detected more than $30m in payments by the consortium for non-existent consultancies. Some of the money may have been bribes to politicians.

Grupo Aval is owned by Luis Carlos Sarmiento, Colombia’s richest man. Its legal adviser for many years was Néstor Humberto Martínez. Since 2016 he has been Colombia’s attorney-general. Odebrecht has admitted in a plea bargain with the United States’ Department of Justice that it paid $11m in bribes to Colombian politicians in order to obtain the Ruta del Sol contract. Both Grupo Aval and Mr Martínez denied prior knowledge of these payments, and of any subsequent ones.

But earlier this year, Mr Pizano gave Noticias Uno, a television programme, recordings he made secretly of conversations he had with Mr Martínez in 2015 regarding the payments for consultancies. Noticias Uno aired them after Mr Pizano’s death. In them, Mr Martínez can be heard promising to inform Mr Sarmiento of the murky payments. In a statement, Mr Martínez said that Mr Pizano could not confirm that those payments were bribes. As matters stand, Aval is blaming Odebrecht for paying the bribes behind its back. But Mr Pizano’s documents and recordings seem to show that the consortium made some sort of shady payments and that Aval at least knew about them.

In 2017 Mr Martinez’s office ordered the house arrest of Luis Fernando Andrade, a former partner at McKinsey, a management consultancy, who was then the director of the government’s infrastructure agency, arguing that he illegally awarded an addendum to the contract to extend Ruta del Sol. Mr Andrade denies any wrongdoing. As Aval’s lawyer, Mr Martínez reviewed that addendum and approved it.

Whatever the truth of Mr Pizano’s allegations, Mr Martínez, who has powerful political backers, is clearly in no position to conduct an impartial investigation into them, as he may have a case to answer himself. Yet he cannot be sacked as attorney-general. He has recused himself from two of many related cases, placing a subordinate in charge. Many Colombians want him to step aside entirely, or resign.