The former agent, Igor Ustymenko, was spotted watching the Kyiv street on the night the bomb that killed Sheremet was planted. He was identified and interviewed in the film "Killing Pavel".
The documentary was released last Wednesday and shows the results of a nine-month long investigation by reporters from OCCRP and Slidstvo.Info.
Ukrainian President Petro Poroshenko announced the questioning in a press conference Sunday, thanking journalists for identifying Ustymenko as a possible witness, according to Interfax Ukraine.
"Unfortunately, I expected more, better result and I’m not pleased with the fact that we still haven’t found the killer and he is not held accountable," Kyiv Post cited Poroshenko as saying.
He claimed that immediately after the murder, he appealed to foreign embassies for assistance in the investigation.
A group of journalists attending the press conference wore T-shirts branded with the words "Who killed Pavel?", according to the Ukrainian Journal.
The Belarusian journalist’s reporting had challenged authorities from Minsk to Moscow and Kyiv.
Sheremet was driving to work on July 20, 2016 when his car exploded. Police have made little progress in solving the murder since.
According to Poroshenko, Ustymenko left Ukraine’s Security Services (SBU) in April 2014 along with 2,000 other former SBU employees, Interfax Ukraine reported.
The President added that if the mass media has any further evidence for the investigation, they are invited to bring it to him, according to Pravda.
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