Complex sentence: On the night of August 23 and into the early morning hours of August 24,1970, Fassnacht was in the lab taking care of unfinished work because he and his family were slated to leave for a vacation in San Diego, California.
Split into simpler sentences: On the night of August 23 and into the early morning hours of August 24,1970, he had gone to the lab to take care of unfinished work. He and his family were slated to leave for a vacation in San Diego, California.