A first post-mortem concluded that Aliyev hanged himself, but his lawyers have called for an investigation into his death.
On the day he was found dead he had been due to testify against two former cell mates accused of blackmailing him with the threat of getting him killed in a way that would look like suicide.
But Austrian authorities said that no examinations so far suggest that there was any third-party involvement in his death. The results of a toxicological report are due in a few days, which will reveal whether at the time of his death his blood contained traces of anything other than his regular heart medication.
Meanwhile, his diary will be translated from Russian into German, to see if it might offer any clues as to his state of mind before his death.
"It has been secured and will be translated," Nina Bussek, spokeswoman for the prosecutor, told the Kurier newspaper on Thursday.
Aliyev’s lawyer, Manfred Ainedter, claims that a page of the diary had been removed. The diary was only found after a thorough search of Aliyev’s single cell, where he had been moved after the alleged threat against him became public.
Ainedter does not believe Aliyev’s death was a suicide. "He had just ordered new glasses. He had a hair appointment on Tuesday. Why would he kill himself?"
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.