Thanks for everyone who posted information from the interview with Sheriff Fitzgerald today.
The interview does seem to lead to a theory this was a blitz of an attack, very fast. I had thought the killer(s) had been in the house for a longer time period before the shooting started, but maybe not. Perhaps the killers went in with guns blazing and a specific motive and target, and a plan to get in and get out fast.
On the other hand, if the the 911 call was made soon after the break in and it was detected by the unsubs a call had been made, it makes me wonder if that was the reason for the quick get away, since they would know law enforcement would be on the scene soon, so hastened the timeline. IMO.