Good point! I also got that impression and that made this story feel shady and finally even boring, resulting in an empty aftershade, mentally.

However, taste modulates wildly.

I think the narrator is the murderer and is lying about the man in the gray tracksuit. The repeated criticism of Aaron's moral character is a sort of rationalization for having killed him, with the underlying motive actually being a combination of greed and envy. Remember that the funds used to kick-start the trading platform came from a hackathon win that Aaron "stole".