During this time his investigative team laid criminal charges against former Ukrainian prime ministers Yulia Tymoshenko and Pavlo Lazarenko.

[3][1] In 2012, Symonenko's investigative team charged former Ukrainian prime ministers Yulia Tymoshenko and Pavlo Lazarenko in a criminal case related to United Energy Systems of Ukraine (UESU).

[3] On 24 December 2020, Symonenko transferred a case of bribery charges against Oleh Tatarov, deputy chief of staff of president Volodymyr Zelenskyy, from the National Anti-Corruption Bureau of Ukraine (NABU) to the SBU.

Later that month, prosecutors under Symonenko's supervision refused to arrest Tatarov, arguing that the grounds were insufficient, while NABU disagreed, stating that the evidence was enough to lay charges.

[6] The Anti-Corruption Action Center interpreted the Ukrainska Pravda investigation to show "absolutely obvious" links between Symonenko and Tatarov.

[4] Symonenko signed the December 2021 treason charges against Petro Poroshenko, former Ukrainian president, during a leave of absence of Iryna Venediktova, Prosecutor General.

Symonenko resigned from this position on 24 January 2023, after a scandal involving another businessman, Hryhoriy Kozlovskyi, and a vacation trip to Spain in December-January, which subsequently led the National Security and Defense Council banning state officials from leaving Ukraine in late January 2023, except for business trips.