What St. Paul police originally thought was a suicide has turned into a homicide investigation after a person was shot inside an apartment in the city's Merriam Park neighborhood on Monday.

Officers went to an apartment building on the 1900 block of Marshall Avenue at about 2 p.m. after somebody called and reported that a man had shot himself. Police found the victim with a gunshot wound to the head and a handgun at the scene, said Sgt. Mike Ernster.

Paramedics pronounced the man dead at the scene, Ernster said.

Investigators spoke with witnesses and noted "inconsistencies with their statements," Ernster said. That led investigators to have probable cause to book an 18-year-old suspect into the Ramsey County jail.

The Ramsey County Medical Examiner will release the name of the victim and the cause of death.

This marks the sixth homicide in St. Paul this year.