Thank-you, Annie, excellent post.
If the murderer is the arsonist, we can assume that he stalks and watches, since LG told us in her interview upthread that they had just retired for the night, when they awoke (presumably from the sound sleep she also started they were in), so, the perp knew they had gone to bed before he set fire.
If we assume stalking and watching, the initial contact site and time could be early afternoon. If the perp was watching Alanna and watching that she was loosely guarded, he was just biding time in the neighborhood.
If either of the black cars is driven by the murderer, I bet they are on camera at different times thought the afternoon, filmed more than once.
As for 2 different black cars, I think LE knows that one of them is not suspicious. But, they want the broadest range of tips on this subject, so, they have released multiple images.
JMO