Russian Lieutenant Lev Stupnikov secretly passed Ukraine information about the positions and activities of Russian military units while serving in the Russian army, according to an investigation by The Wall Street Journal.
The newspaper reported that Stupnikov provided the Ukrainian side with coordinates of military sites, information about command posts and other intelligence that was used to carry out strikes.
The WSJ said information supplied by Stupnikov contributed to attacks that killed more than 300 Russian military personnel in total. That overall figure has not been independently confirmed.
In one episode described by the WSJ, information provided by Stupnikov was followed by a Ukrainian strike that, according to the newspaper, killed 68 Russian troops and wounded roughly 60 more.
Stupnikov later left Russian positions and crossed into Ukrainian-controlled territory.
The circumstances and estimates described in the article are based on The Wall Street Journal’s investigation and interviews.