And if they all use garage as entry - it might have been a few minutes before they checked front porch. In other words, the blood might have been found AFTER going in via garage (or via open back door for that matter) quick walk through house,’checking swimming pool maybe, then going around to front door - and calling 911 immediately once they saw blood and removed camera.
(I’d have assumed front porch would be first arrival point for family, but now hearing garage entry, I realize it may well not have been.)