I don't buy that Oleg was 'our guy' - it doesn't make any sense, because its about someone working in the US.
Other options include
Sergei Millian
George Nader
Rinat Ahkmanshin - the russian translator at the Trump tower meeting
As for the dead guy - here is a list of potentials
https://www.cnn.com/2017/03/24/europe/dead-russians/index.html
On the morning of the US election, November 8, about an hour after the first polls opened in New York City, police received a 911 call about an unconscious man inside the Russian consulate. When they arrived, they found Sergei Krivov, 63, unresponsive.
Russia's ambassador to Turkey, Andrey Karlov, 62, was assassinated in Ankara on December 20. He was shot at point-blank range by a gunman while speaking at an art exhibition. The shooter, who was a Turkish police officer, shouted "do not forget Syria" during the assassination.
The same day as Karlov's killing, Petr Polshikov, 56, a senior Russian diplomat, was shot to death in his Moscow home, according to Moscow newspaper Moskovskij Komsomolets. The paper said Polshikov's wife found him in their bedroom with a pillow over his head. Underneath the pillow, police found Polshikov with a head wound.
Andrey Malanin, a senior diplomat at the Russian embassy in Greece, was found dead in early January.
Vitaly Churkin, 64, Russia's ambassador to the United Nations, died on February 20 of an apparent heart attack. He was "in his office fulfilling his duties" when he died, according to a statement from the Russian mission at the UN.
Denis Voronenkov, 45, was gunned down Thursday outside a hotel in Kiev. Voronenkov and his wife both spoke out against Russian President Vladimir Putin after they left Russia for Ukraine in October.