Looking at that video, it sure seems deliberate and planned. I was reminded of a case from many years ago where an ex-girlfriend of the victim's husband stalked, kidnapped and murdered the wife of her former boyfriend. Even though this couple seemed happily married at the time, some people are slow and methodical in their plans for revenge.
Usually, garage sales are advertised in news circulars, etc., and most people are out earlier setting them up. I hope LE is checking phone records from days leading up to sale. She may have contacted the victim earlier regarding that particular garage sale and items being sold. It's not difficult to find out names and phone numbers if an address is listed for the sale. ALL MOO.
I only hope LE is all over this and knows a lot more than the public. Hopefully, an arrest warrant is ready to be served.