The Bulgarian authorities have reopened a criminal investigation into the poisoning of a prominent arms dealer over questions about a possible connection with the nerve agent attack on Sergei V. Skripal, the former Russian spy poisoned in Britain last year.

Bulgaria’s chief prosecutor, Sotir Tsatsarov, said Monday that a suspected Russian intelligence officer, identified in news reports last week as potentially involved in the Skripal case, had also visited Bulgaria in April 2015, around the time that the arms dealer, Emilian Gebrev, was poisoned with an unknown substance.

Last week, the British newspaper The Telegraph reported that the two men indicted in the poisoning — identified by British authorities as active officers in Russia’s military intelligence agency — were accompanied by a third man, an officer using the alias Sergey Fedotov, when they traveled to Britain last spring. In his remarks on Monday, Mr. Tsatsarov said the same man had visited Bulgaria three times in 2015, confirming a report published last week by the investigative site Bellingcat.

“We are trying to establish all moments while he was on Bulgarian territory, the hotels he stayed in, the vehicles he used, contacts with Bulgarian citizens,” Mr. Tsatsarov said at a news conference.