W/O Urho Lehtovaara - cause of death

Anyone there who can confirm the cause of death of W/O Urho Lehtovaara, Knight of the Mannerheim Cross ?

Wikipedia claims he died in the cell of "Red Valpo" (Finnish Security Police, controlled by Communists at the time) suspected of participating in the famous Arms Cache Case.

I have been led to believe he died by his own hand either in Suomusjärvi (or Siilinjärvi)