Over time, Vaptsarov absorbed a lot of Communist ideas and started taking an active part in the ideological movement. In 1940, he participated in the so-called "Sobolev action," gathering signatures for a pact of friendship between Bulgaria and the USSR. The illegal activity earned him an arrest and an internment in the village of Godech. After his release in September 1940, Vaptsarov got involved with the Central Military Committee of the Bulgarian Communist Party. His task was to organize the supply of guns and documents for the communist resistance. He was arrested in March 1942. On 23 July 1942, he was sentenced to death and shot down on the same evening along with 11 other men.