Krasnodar regional authorities said Tuesday that notorious gang leader Sergei Tsapok, who died in prison on Sunday night, had succumbed to acute heart failure caused by the blockage of a pulmonary artery, Interfax reported.
Tsapok, who is believed to have led a criminal organization since the early 2000s, was convicted last year of organizing the murders of a wealthy farmer and 11 of his family members and friends in the town of Kushchyovskaya in 2010. The massacre, in which several young children were brutally killed, sparked outrage across Russia. Tsapok was sentenced to life in prison for his role in those murders and other crimes.
The 38-year-old gang leader had been taken to a hospital over the weekend where he was preliminarily diagnosed with a stroke before being returned to the medical facilities of his prison. His body was discovered in his cell on Monday morning, according to Russia's Investigative Committee.
Tsapok is the fourth member of his gang to die in prison. Three other members of his crime organization took their lives while in detention, RIA Novosti reported.