Does retzicha only include intentional murder?
Retzicha refers strictly to unlawful murder. Putting someone to death is harigah, not retzicha.
If it was purely an accident, then I’d say no — he is a “horeg” but not a “rotzeach.” If he was a shogeg (i.e. at least partially negligent), then I’d say yes (the Torah uses the term for someone who must flee to one of the Arei Miklat).
The Wolf