Complex sentence: They had not slept at all on the previous day, and they had been drinking heavily: in an autopsy, pilot Hattinen had a blood alcohol level of 2 ‰, whilst co-pilot Halme had a blood alcohol level of 1.56 ‰.
Split into simpler sentences: They had not slept at all on the previous day, and they had been drinking. In an autopsy, pilot Hattinen had a blood alcohol level of 2 ‰, whilst co-pilot Halme had a blood alcohol level of 1.56 ‰.