he's killing for the sole sake of the sadistic entertainment value in breaking a woman's mind.
I'm not sure it's simple sadism. He's crushing a voice of dissent in his mining operation. Word will spread, and it'll be a long time before anyone claims to smell another gas leak. He's lost a few workers, but the rest will learn to fear him.
Of course this is all based on the assumption that it's Asquith. Could easily be a completely new character, or a different old character. Hey, maybe it's Blue Snowman in a REALLY good male-impersonator disguise!