Complex sentence: Müller cooperated with the investigation and pled guilty to throwing the Molotov cocktail; however he claimed that he was told by Lukeš that the targeted house was not inhabited and that it was merely a storehouse of stolen goods.
Split into simpler sentences: Müller cooperated with the investigation and pled guilty to throwing the Molotov cocktail. However, he claimed that he was told by Lukeš that the targeted house was not inhabited, and that it was merely a storehouse of stolen goods.