A key witness in a bribery case that has brought down several of Moscow’s senior crime-fighting officials has been shot dead in his car outside St. Petersburg.

Businessman Badri Shengelia, 53, testified in court last February that he had paid Mikhail Maximenko, the head of security at Moscow’s Investigative Committee, $50,000 in 2015 to launch a criminal probe. Maximenko was sentenced to 13 years in 2018 for receiving a $500,000 bribe from a notorious mob boss to soften the sentences of gang members involved in a restaurant shootout.

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Investigators opened a murder case on Monday after Shengelia’s body was found with several gunshot wounds inside a Mercedes on a St. Petersburg highway.

The Fontanka news website reported that Shengelia’s car had been shot at least six times from an unidentified vehicle.

Interfax quoted an unnamed source as saying the investigation will look into any connections between Shengelia’s murder and his admission to paying a bribe to Maximenko, among other leads.

The $500,000 bribery case implicated the former deputy head of Moscow's Investigative Committee, Denis Nikandrov, who was handed a jail sentence of 5.5 years in the case last month and his retired ex-boss Alexander Drymanov, who was arrested on the same charges this summer. Maximenko’s deputy head of security was also sentenced to 5 years behind bars.