Right now, heartfelt condolences to the families and loved ones of the slain officers, and prayers for those officers who are injured.
We will have the facts in time, but for now, these officers and their families deserve our prayers.
And these were probably night shift officers who would probably be going home right after their work there ended.
I find the timing very peculiar as well. 5:00 AM? Unless the start time was changed and staggered for some companies in an effort to reduce road congestion the usual start time has traditionally been 7:00 AM with the last buses leaving at 6:30-6:45 (depending on the distance from parking lot to the refinery) which gives workers sufficient time to "swipe in" at the turnstiles and then get to the job site. (which usually means another bus ride on buses already "in plant" to the unit being worked on so that the incoming bus doesn't have to be inspected every time it enters the plant).
Otherwise somebody was there very early to catch the bus in.