Who played the hitman?

That opening scene took a surprising turn. But who is the actor that plays the hitman? He's referred to as "Dan" and "Mr. McGuire" throughout. There aren't really credits on the film itself (at least the Vinegar Syndrome DVD I watched) and credits at IMDB are sparse. I see in reviews people saying he's William Guhl, but that name isn't in the credits at all. There's a William Connors and a William Gary listed.

Anyone know who this actor actually is? Guy on the right in the second picture.

https://www.imdb.com/title/tt0066426/mediaviewer/rm236070657/

https://www.imdb.com/title/tt0066426/mediaviewer/rm152184577/