Complex sentence: Solonik and a fellow criminal were apprehended by Moscow police when they were having a drink at a marketplace, but the police failed to check Solonik thoroughly, and he opened fire in the police station with a small automatic weapon which he concealed under a raincoat.
Split into simpler sentences: Solonik and a fellow criminal were apprehended by the Moscow police when they were having a drink at a Moscow marketplace. The police failed to check Solonik thoroughly, and he opened fire in the police station with a small automatic weapon which he concealed under a raincoat.