Complex sentence: They had not slept well in the previous night, and they had been drinking heavily: in his autopsy, pilot Hattinen had a blood alcohol content of 0.20 (2 ‰), whilst co-pilot Halme had a BAC of 0.156 (1.56 ‰).
Split into simpler sentences: They had not slept well in the previous night, and they had been drinking heavily. Autopsies revealed that pilot Hattinen had a blood alcohol content of 0.20 (2 ‰), whilst co-pilot Halme had a BAC of 0.156 (1.56 ‰).