FERGUSON, Mo. (AP) — Two men died early Tuesday in a shooting that involved a police officer in Ferguson, Missouri.

St. Louis County police are investigating the shooting that happened just before 1:30 a.m. Police said in a news release that a Ferguson officer was walking out of a gas station and heard gunshots, then saw a man shooting at another man.

The Ferguson officer fired his service weapon at the shooter, St. Louis County police said. One man collapsed near a gas pump. The other ran onto West Florissant Avenue before collapsing. Both men were pronounced dead at the scene. No information about them has been released.

It wasn’t immediately clear if the officer or the other man killed the man police say was shooting. Police said the investigation is ongoing and no further information on the shooting was immediately available.

Investigators said the men apparently knew each other. The Ferguson officer, a 37-year-old with nine years of police experience, was unhurt.