Waco police on Friday arrested the 41-year-old boyfriend on a murder charge.
Officers responded to a domestic dispute Thursday night and found the body of 25-year-old Zachary Davis on a sidewalk.
Investigators say Davis, who was visiting the couple, had intervened to protect his 27-year-old sister as she allegedly was being assaulted by Allan Story.
Police say the two men struggled and Davis was stabbed with a knife. His sister wasn't hurt.
Story fled, but was captured by police about four hours later.
Sgt. W. Patrick Swanton says Story was jailed facing arraignment. Police had no information on an attorney for the suspect.
