This information came from Aliyev’s lawyer, Manfred Ainedter, who contrary to what prosecutors have said believes his client was murdered.
He told Ö1 that the sedative which showed up in a toxicological report is banned in Austria, which he said made it impossible that Aliyev had been prescribed the drug by prison doctors.
Nina Bussek, the spokeswoman for the prosecutor, could not confirm the report due to the ongoing investigation.
Vienna’s deputy chief prosecutor Gerhard Jarosch has said that there will be a comprehensive investigation into Aliyev’s death “regardless of cost - we don’t want to expose ourselves to any allegations that we have omitted anything”.
An initial post mortem found no evidence of foul play.
Aliyev did not leave a suicide note but a diary was found in his cell, written in Cyrillic script. Jarosch said that it was being translated to see if it could yield any clue to Aliyev’s state of mind before his death.
On the day he was found dead he had been due to testify against two former cellmates accused of blackmailing him with the threat of getting him killed in a way that would look like suicide.
Aliyev, who was once married to a daughter of Kazakh President Nursultan Nazarbayev, was jailed in absentia in Kazakhstan for seeking to oust the government.
He was in prison in Vienna awaiting trial for the murder of two bankers in Kazakhstan - a charge which he said was politically motivated.
Austria had refused requests to extradite Aliyev, who was sacked as Kazakh ambassador to Vienna in 2007.
Austria's Green party has called for a thorough examination of prison surveillance cameras and logs, to confirm whether or not anybody entered his cell during the night.