Complex sentence: Because of the remote area and the difficult access where the crash occurred, it took rescue personnel 12 hours to reach the site itself, and after they reached the crash site, the investigations begun to find the causes of the crash of the 737.
Split into simpler sentences: Because of the remoteness of the area and the difficulty of access, it took rescue personnel 12 hours to reach the site. After they reached the crash site, the investigation began to find the causes of the crash of the 737.