Complex sentence: The two claimed having not left the apartment after the meeting with Li, which is contradicted by eyewitnesses testimonies, after which Li had been seen elsewhere at the time when the purported meeting with the two took place.
Split into simpler sentences: The two claimed having not left the apartment after the meeting with Li. However these claims contradict eyewitnesses testimonies, after which Li had been seen elsewhere at the time when the purported meeting with the two took place.