The attacker was apparently looking for his girlfriend and had gone to her former boyfriend's apartment Monday where the victim was a guest.
KXRO reports he left the carcass behind.
Police later found the 33-year-old Hoquiam man arguing with his girlfriend at another location and arrested him after a fight.
He said he had found the marten dead near Hoquiam, but police don't know why he carried it with him.
A marten is a member of the weasel family.