B-Hebrew: The Biblical Hebrew Forum

Ducky writes

I wonder if "by day" is the right way to see it.
Maybe it comes to say that he kills at the beginning of the morning.

Possibly, but first he eats breakfast.

Isaac Fried, Boston University
www.hebrewetymology.com

I'm saying that because some see this part focus on the idea of people who "work" only in the darkness, and "hide from the light.
So if we go that way, then we need to see that the killer also "hides" from the light, and so, maybe the meaning is "in the first light", or "before the light".

I think the meaning is "darkness" like with other sinners that "didn't know light" (job 24;16), or better at sunset in the beginning of the murderer's "work day".