Russia claims Alexei Navalny died of 'sudden death syndrome' as mother searches for body

Russian opposition leader Alexei Navalny died from a heart attack at a Siberian penal colony where temperatures plummet to -30C, it is claimed.

Investigators told his mother Lyudmila Navalnaya her 47-year-old son had died from sudden arrhythmic death syndrome, though this cause of death has not been independently verified.