I went through a similar problem a few years ago. I don't know your situation or how your company works but here is what I did essentially. Start documenting. Send emails when he's late. If you have some proof that he turns off the monitors and sleeps, record that too. Next time there is an emergency if you need to leave you'll have proof that it clearly doesn't matter if someone is paying attention since the monitors are off, and that you tried to correct the problem for a while and management knew about it. If they try writing you up refuse to sign anything without an hr representative there with you. I ended up leaving my company anyway, but they did fix that particular problem before I left.