Complex sentence: Stevens was the first U.S. ambassador to die in office since the 1988 aircrash in Pakistan which killed Arnold Lewis Raphel; he was the eighth U.S. Ambassador to be killed in the line of duty.
Split into simpler sentences: Stevens was the first U.S. ambassador to die in office since the 1988 aircrash in Pakistan which killed Arnold Lewis Raphel. Stevens is the eighth U.S. Ambassador to be killed in the line of duty.