They suspect Tokyo’s bidding committee bribed the Diacks in 2013 to secure votes, which the committee has denied.
Sebastian Coe, Diack’s successor, has undertaken to rebuild trust in athletics and has introduced changes to the sport’s governance.
Lamine Diack, the disgraced former head of athletics’ governing body, goes on trial in Paris on Monday (June 8) on charges of corruption and money laundering linked to a Russian doping scandal.
Prosecutors allege he solicited €3.45 million (S$5.43 million) from athletes suspected of doping to cover up the allegations and allow them to continue competing, including in the 2012 London Olympics
Diack, who turned 87 on Sunday, has denied wrongdoing. His lawyers have said the accusations are baseless.
Diack, from Senegal, led the International Association of Athletics Federations (IAAF), now renamed World Athletics, from 1999-2015 and was among the most influential men in the world sport. He lives under house arrest in Paris and faces a jail sentence of up to 10 years if convicted.
The trial had been due to start in January but was postponed after new documents containing testimony from his son and co-defendant, Papa Massata Diack, were submitted to the court.
Senegal has refused to extradite Papa Massata, who worked as a marketing consultant for the IAAF. The younger Diack also faces charges of money laundering, corruption and breach of trust, according to the indictment, and will be tried in absentia.
The other defendants are Habib Cisse, Diack’s former lawyer at the IAAF; Gabriel Dolle, who oversaw doping tests at the IAAF; and Russians Valentin Balakhnitchev and Alexei Melnikov, who were Russia’s athletics’ federation chief and head athletics coach respectively at the time of the alleged cover-up.
Investigators at the French National Financial Prosecutor’s Office (PNF) describe a web of corruption in world athletics under Diack’s leadership.
In a separate case, French prosecutors are investigating alleged bribes related to the Olympics and World Athletics Championships.