Turkey's Justice Ministry appointed two inspectors to investigate if any violations occurred in the treatment of Kuddisi Okkir, who was detained under the Ergenekon probe and released prior to his death.
Okkir, who was arrested under the Ergenekon probe 13 months ago, died on Sunday, six days after he was transferred to hospital for treatment.
Okkir's wife, Sabriye Okkir, has accused officials of being responsible for her husband's death, adding her husband was taken to hospital from hospital until he was diagnosed. She said her husband's cancer spread to his brain from lungs due to the delay in the treatment and diagnoses.
"My husband went into have a check-up after he was detained. If you look at his report, you would see that he did not have any health problems (before taken into custody)," she told reporters at a news conference on Tuesday.
Okkir's lawyer said the situation regarding Kuddusi Okkir is "a serious violation to human rights." Sabriye Okkir earlier had said she plans to take the issue to the European Court of Human Rights.
Okkir was claimed to be the "financial source" of the so-called Ergenekon organization.
Okkir's death sparked harsh criticism across the country since the lack of a long waited indictment hastened the death of a previously healthy man. His family says the negligence of officials caused Okkir's death, and they are the ones who should be blamed.
The lack of an indictment also raised questions and lead to speculation that the government's efforts to suppress its opponents were the basis for the investigation.