Spoiler, click to toggle visibilty
Do not know if the first part is a spoiler, but he is the "Swordsman" in the comics, an anti-hero whom has been part of the avengers as well as a villain. He has been a mentor to Hawkeye, and what his role continuing the series might be we'll see soon. Now with the points in the show seemingly aiming for Jack, I believe this to be a clear red-harring, and that he might turn into an ally of Kate and Clint going forward. Mrs. Bishop however ... she is shahdy as hell.
A very definite possibility, especially given:
Spoiler: double spoilers because this is from the run that this show is cribbing heavily from (click to see content)
in the Fraction/Aja/Wu Hawkeye series, a big reveal towards the end is that Kate's dad is a member of the consortium of rich assholes working with the Kingpin and the Tracksuit Draculas in the big real estate/gentrification scheme explored over the course of the book. The final issue even has Kate's dad at a meeting of the evil dickbags signing off on a proposal to have her killed (earlier in the series she found out he was involved in the criminal conspiracy and this scene basically served to underline the fact that she is already dead to him).
Of course, the show has changed things such that Kate's dad died years ago, and so her mom is the big rich and powerful CEO. But things could very well turn out roughly the same way.
Beyond the comics, though, not-quite-Swordsman-but-obviously-very-close is so obviously being signposted as the murderer that I'd be more surprised than not at this point if they just played it straight instead of going with a swerve.