Slip or Trip?

Queenie: "Something terrible happened- Arthur slipped and fell on the stairs. He was coming down for another drink- he still had the glass in his hand- and I think he's dead. OMG! What shall I do?"

The autopsy concluded that Arthur had died from a wound on the head, and confirmed the fact that he'd been drunk.

What do you think happened?

Be sure to point to specific evidence from the picture to support your position.