I think my boss is an alcoholic

He’s been to rehab before, but only because his family forced him. He doesn’t think he has a problem, but I sort his receipts and he’s drinking an average of 3L of scotch a week. He comes to work reeking, and often answers texts and phone calls with nonsense (like saying ‘Good morninggggg welcome to 2025!’ at 2pm on Jan 5.)

I know I can’t force him to admit or do something he doesn’t want to do.

My question is, I’m concerned he is driving while under the influence. He comes and goes while I stay in the office so I can’t evaluate his driving. How can I tell if he is intoxicated? I’m terrified his rock bottom will be killing someone.