(Bloomberg) -- Bulgarian authorities are investigating possible connections between a 2015 poisoning and the attack last year against a former Russian spy in the U.K.

Police in Bulgaria are coordinating with British law enforcement in the probe of the non-fatal poisoning of three people connected to a weapons plant; the owner, his son and an executive, Chief Prosecutor Sotir Tsatsarov told reporters in Sofia on Monday.

Emilian Gebrev, the head of small-arms and ammunition maker Emco OOD, asked authorities to resume the investigation suspended in 2016 because he believes the poison was similar to the one used to attack Sergei Skripal and his daughter in the English city of Salisbury in March, Tsatsarov said.

A test by an independent laboratory in Finland showed the presence of a strong pesticide in Gebrev’s samples, though no substances banned by the Chemical Weapons Convention, according to the prosecutor.

Bulgarian prosecutors found that Sergei Fedotov, a Russian citizen suspected by U.K. authorities of having a connection to the Skripal case, visited Bulgaria several times in 2015, Tsatsarov said. Bulgaria didn’t join most European Union countries in expelling Russian diplomats last year after the U.K. poisoning case. The government then said it needed more proof of Russia’s involvement in the attack.

The Russian government denied any knowledge of the case. “There’s only one question: how is it possible that the use of some chemical warfare agent in Europe goes unnoticed in 2015? Why did we find this out only now?” Kremlin spokesman Dmitry Peskov told reporters on Friday.

--With assistance from Tony Halpin.

To contact the reporter on this story: Slav Okov in Sofia at sokov@bloomberg.net

To contact the editors responsible for this story: Balazs Penz at bpenz@bloomberg.net, Scott Rose

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