Witness testimony and evidence has already been collected as part of an investigation into the murder of former Ukrainian parliamentarian Oleh Kalashnikov and journalist Oles Buzyna, the Ukrainian interior minister's advisor Anton Heraschenko has said, expressing hope that those who committed these crimes will be found.

"The best specialists of the criminal investigation department and the best detectives of the Interior Ministry are probing the murder of Oleh Kalashnikov and Oles Buzyna. Witness testimony and material evidence has already been collected in both cases. It means there is hope that those who perpetrated, masterminded and ordered [the killings] will be identified," Heraschenko said on his Facebook account on Friday.

Heraschenko told the 112. Ukraine television station that several witnesses saw unknown "people hanging around the houses of Buzyna and Kalashnikov."

"Buzyna and Kalashnikov were killed with different weapons," he said.

However, there is no evidence "proving that these murders are linked," Heraschenko said.

"It is possible to say that they [the murders of Buzyna and Kalashnikov] have something in common. But there is no evidence proving this [the link between them]," he said.