The attorney-general’s office in Colombia has opened an investigation into the death of Jorge Enrique Pizano.
Mr Pizano was a key witness in a corruption investigation involving Brazilian construction giant Odebrecht.
He died on Thursday of what forensic experts originally described as a heart attack.
But investigators became suspicious when Mr Pizano’s son died three days later of poisoning after drinking from a bottle left at his father’s home.
Alejandro Pizano had travelled from Barcelona, where he works as an architect, to Colombia to attend his father’s funeral.
While at the family home north of the capital, Bogotá, he took a swig from a bottle of flavoured water which was standing on his father’s desk.
Witnesses said he immediately became violently ill and died on the way to hospital. Doctors diagnosed cyanide poisoning.
His poisoning has led investigators to re-examine the forensic tests carried out on his father’s body.
The possibility that Jorge Enrique Pizano’s death may not have been due to natural causes has caused a stir in Colombia with many speculating about who could have wanted to silence the engineer.