Friday's incident sparked a brief panic at Union Station in Washington, D.C., AFP reported on Saturday.
Rail service at Union Station, a main Amtrak hub on the US East Coast rail line linking Boston, New York and Washington, resumed shortly after the incident.
Police commander Jeff Brown told reporters the suspect apparently had stabbed a woman at the entrance to an adjacent building, and was then chased into the station by an armed security officer from the adjacent Securities and Exchange Commission.
The officer fired one round when the suspect refused to surrender his weapon and lunged toward him.
The suspect was hit in the side, and his injuries - along with those of the woman - were not life-threatening, he said. Both were being treated at area hospitals.
"We believe this is a domestic-related incident," Brown said. "There is no active shooter, there was no active shooter. This was an isolated incident."