The 30-year-old man — identified only as Michal M., in line with Poland's privacy laws — was convicted in Jelenia Gora over the killings in the town in March 2013. The victims were found dead inside the building of the Lower Silesia Philharmonic, where the man was employed.
The 60-year-old guard was found near the building's entrance and the 27-year-old harpist in the guest room. She had travelled to the western town to play one concert.
Poland does not have the death penalty. The verdict is subject to appeal.