Normally, I would agree but not this time.
The ex-husband has an alibi. Her ex-husband, who has remarried, was with his family at his son's football game. Heidi left at halftime. So he was there at least another hour or so. Her dog was found 3 hours after she left Downey where the football game was held. That's a tight window.
And it's unusual for the FBI (not just local LE) plus the Elite Robbery and Homicide unit of the LAPD to show up at the home of a missing person - all of whom entered with guns drawn.
LE knew she wasn't there. Her ex-husband and a friend, who let him in, had already been in the home during the two weeks she was missing before LE finally showed up. That has been reported in news reports linked several times in this thread.