(Bloomberg) -- Mexican President Andres Manuel Lopez Obrador said Wednesday his two predecessors should testify about corruption allegations made by a key witness in a bribery case.

Lopez Obrador said testimony from a former Pemex chief, Emilio Lozoya, seems to implicate not only former President Enrique Pena Nieto in alleged bribery, but also the previous president, Felipe Calderon. But unlike Pena Nieto, Calderon isn’t referred to directly in Lozoya’s testimony that was made public by Attorney General Alejandro Gertz on Tuesday.

Calderon, and several of his former representatives, didn’t immediately respond to a request for comment. Three former representatives of Pena Nieto declined to comment.

Lopez Obrador, who claims he was robbed of the presidency by fraud when he narrowly lost to Calderon in 2006, has publicly attacked Calderon on several occasions. The expanding reach of investigations that have emerged from a corruption case against Lozoya promise to dominate political discussion in Mexico ahead of mid-term elections next year, where Lopez Obrador’s party will be defending its majority in the lower house of congress.

“Yesterday the attorney general made known that ex-presidents, two ex-presidents, as I understood it, are involved in possible acts of corruption,” Lopez Obrador said about both Calderon and Pena Nieto. “What’s next? Well, that they be summoned to testify and that Mr. Lozoya present the evidence.”

Lopez Obrador did not provide further details on what alleged acts of corruption may have touched the Calderon administration. In a video message Tuesday, Gertz said Lozoya testified that during the Calderon administration, the Etileno XXI petrochemical plant, a project of Odebrecht unit Braskem and Mexico’s Grupo Idesa, received “economic benefits” and privileges in the prices of supplies, which caused losses for the government.

In the same video, Gertz said Lozoya had directly implicated Pena Nieto and his finance minister in funneling bribes from Brazilian builder Odebrecht into the presidential 2012 campaign, as well as ordering Lozoya to pay off Mexican lawmakers to back an energy and an electoral reform.

Lozoya said he has at least one video backing his claims as well as four witnesses, the attorney general said. Lopez Obrador said such evidence should be made known.

“We need to take care of due process, but these things need to be made transparent,” Lopez Obrador said.

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