Altynbek Sarsenbaiuly, co-chairman of the Nagyz Ak Zhol opposition party, was found shot dead in his car last February, alongside his driver and bodyguard.
Toguzbayev had alleged in his blog that Nazarbayev's allies were behind the murder. In one article, he wrote that "in a certain sense Nazarbayev is the killer".
Sarsenbaiuly and other opposition leaders had denounced earlier presidential elections as fraudulent.
His death was officially blamed on a dispute with a civil servant, but the opposition accused Nazarbayev's government of staging a cover-up.
Ten people, including state security officers, were jailed last year, but the opposition criticised their trial, saying it was designed to conceal Sarsenbaiuly's real killers.
Sarsenbaiuly was not the first critic of Nazarbayev, who has held power since 1989, to be found dead.
Three months previously, Zamanbek Nurkadilov, a former mayor of Almaty, the Kazakh capital, and a critic of Nazarbayev, had been found dead at his home.
Nurkadilov was found with two bullet wounds to the chest and one to his head.
An official investigation concluded that his death was suicide.