In 1927 he moved to Warsaw and began teaching at Mieczysław Karłowicz's school as well as playing violin in theatre orchestras.
[4] One of his first major works was the music for Noah Pandre (נח פאנדרע) by Zalman Shneur, produced by Zygmunt Turkow at the Nowości Theatre; he followed with music for Di kishef-makher (The sorcerer) by Klara Segałowicz; Soreh-Sheyndl fun Yehupetz directed by Ida Kamińska; Meylekh-freylekh by Yankev Preger, produced by Michał Weichert in 1938 in Łódź, later in Warsaw; revue programs for Shimon Dzigan and Israel Shumacher's revi-teater.
His greatest artistic success was the musical score to Lope de Vega's Fuenteovejuna, a show produced by Ida Kamińska's theatre company.
[2] At the outbreak of World War II, Szajewicz fled to Białystok, where he was chosen to lead the symphonic orchestra.
When German-Soviet war broke out in 1941 he wasn’t able to evacuate; he headed back to Warsaw to be with his mother, but somewhere in the woods between Białystok and Baranowicze he died in unknown circumstances.