In 1946, Kwas was arrested and imprisoned in Kielce prison. He was subjected to a brutal interrogation. On 13 September, under unclear circumstances, he was shot in his cell by a guard and died shortly thereafter. The funeral was attended not only by Scouts from the Kielce "Gray Ranks" but also by numerous Scouts from all units, as well as schoolchildren, acquaintances, and friends. He was buried at the Old Cemetery in Kielce.

Since 1993, the street running along the Old Cemetery, near his grave, formerly that of [Soviet General] Ivan Konev, has been named after him.

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