"So far, we have not received [Onyshchenko’s] consent to hand over these tapes... He also appears on these recordings as an accomplice... The ball is now in his court," Sytnyk said.
According to him, NABU detectives continue communicating with Onyshchenko via text messaging.
"There is a ruling of the Spanish court to extradite Onyshchenko. However, it has not yet entered into force as it was appealed against," the law enforcer said.
"We still expect that Mr. Onyshchenko will elaborate on a specific case that ‘I paid lawmaker so-and-so a certain amount for passing such-and such law,’ so that this could at least be checked. It's very difficult to check general terms," the anti-corruption crusader said.
He stressed that in order to establish the truth, the records must be introduced into evidence in a lawful way to make further expert examinations possible.
"And this process depends not only on the law enforcement agencies but primarily on Onyshchenko himself. So far, we have not received consent from him to pass any of these wiretaps in any lawful way ... He also appears on these recordings as an accomplice but I have no idea whether he understands it or not," Sytnyk said.
He added that "when it comes to specific testimony, specific names, he starts playing some confusing game – no specific testimony, no tapes in a lawful way."
"But extradition does not mean that the [recording] device and the wiretaps themselves will be brought along with him," Sytnyk said.
On March 16, 2016, the NABU raided the office of Onyshchenko. It stated the searches were carried out under the pre-trial investigation into abuse of office during the sale of natural gas extracted jointly with Ukrhazvydobuvannia SE.
Later, the NABU requested the Prosecutor General's Office (PGO) to remove the immunity from people's deputy Onyshchenko. Moreover, the NABU and the PGO claim Onyshchenko is involved in embezzlement of 1.6 billion hryvnia (approx. $64.02 million).
On June 16, 2016, Prosecutor General Yurii Lutsenko issued a motion requesting Verkhovna Rada's consent for criminal prosecution, arrest, and pre-trial detention of Onyshchenko. On July 5, 2016, the parliament approved the detention and arrest of the lawmaker.
The suspect himself stated he was busy with the preparation for the upcoming Olympics and not going to react to NABU's actions. On July 29, 2016, Onyshchenko said he was in the U.K. and had applied for political asylum.
Read more: MP Onyshchenko has records of Poroshenko discussing buying votes and Ukrhazvydobuvannia's shadow dividends, - Dzerkalo Tyzhnia
On Dec. 1, 2016, the Security Service of Ukraine (SBU) announced it suspected fugitive MP Onyshchenko of high treason. As noted, the MP acquired Russian citizenship in exchange for cooperation with Russian authorities to destabilize the situation in Ukraine. On the same day, Onyshchenko said he had provided compromising materials against President Poroshenko to the U.S. intelligence.