It didn't occur to me at the time but how Vinters died is a very interesting question. As the a result of a Pact between Nazi Germany and Soviet Russia, which amongst other things carved up Europe between the signatories, the Soviet Union invaded Latvia on 16 June 1940. Following the invasion Soviet forces unleashed a reign of terror including the deportation or murder of members of parliament, the civil service and the army. This systematic repression culminated in the mass deportation of 15,600 men, women and children on 13-14 June 1941. In total 35,000 people were deported during the first occupation. See http://goo.gl/Q4BYl
According to Latvian Wikipedia, during this first Soviet occupation 800 Army officers and NCOs were arrested and 682 of those were murdered including 19 generals, 44 colonels, 109 Lt. Cols, 195 captains, 145 first lieutenants and 142 lieutenants. In addition a total 4665 Latvian soldiers (or about 15% of prewar armed forces) were deported to the Gulag. See http://goo.gl/fS62r .
Some lists of those lost during the occupation exist but they are difficult to access and not complete. So far I have not found any proof that Vinters was amongst those liquidated but his death in 1941 (if that date is correct) would be quite a coincidence. Given his intelligence links as revealed by VJK together with his support for Polish freedom, Vinters would have been a prime candidate for NKVD firing squads. Of course this is just conjecture and I will keep digging to see if I can confirm how he died.