It's not all about physical evidence, it's about the entire picture:
AM was at the scene around the time of the murders and he lied about it. He bribed Shelley to lie for him about timing to support his alibi.
The clothes he was wearing are missing. (Tried to influence Blanca to lie about what shirt he was wearing.)
One of his weapons is missing. He hid a raincoat (with gunshot residue on the inside) at his mother's house.
He fiddled with his son's phone "to do something" before even checking on his wife who was lying there, likely dead.
Based on OnStar and phone records, he had only 19 seconds to stop his vehicle; get out of the car; take in the scene; walk to Paul's body; try to turn him over & take his pulse; fiddle with Paul's phone; walk to Maggie's body; check her pulse and call 911. Well I guess that wouldn't be a problem if you had already seen them dead and didn't really need to check them and absorb the shock.
He called Rogan
multiple times before first responders arrived. He was clearly concerned about the video. (also why he was checking Paul's phone.)
ETA: (as someone reminded me above) AM deleted the call log on his phone.
AM showed no emotional concern about catching the killers (even to first responders or detectives).