Complex sentence: Various conspiracy theories about the crash have since been in circulation, and are promoted by senior political figures in Poland, who claim the crash was a political assassination, but no evidence supporting this version was found in Polish and international investigations.
Split into simpler sentences: Various conspiracy theories about the crash have since been in circulation, and are promoted by senior political figures in Poland, who claim the crash was a political assassination. No evidence supporting this version was found in Polish and international investigations.