Authorities responded to the shooting in the 1100 block of N. Del Sol Lane near High Knob Road about 10:30 a.m. and found the shooting victim.
He was declared dead at the scene. His name has not been released.
Investigators said it was an argument between roommates that turned deadly.
Police say a suspect is in custody, but no further information was available.
Friends say the 39-year-old victim used to live at the home with the 23-year-old shooter, but that the older man was asked to leave last week after the two apparently had some sort of falling out.
Neighbors said the victim showed up Thursday morning and began fighting with his former roommate in the driveway and suddenly there was gunfire.
"Carl's a friend of mine, I love him like a son, and he got in the middle of the situation," said neighbor Marie Aguinaga. "There were maybe some threats. I think this man that got shot was out for revenge for some reason and I don't know the reasons why."
"We passed by and we saw the guy there on the floor," said another neighbor, Elizabeth Salinas. "We were shocked."
Authorities have not yet released the name of the victim.
Detectives said they didn't know if it was murder or possibly in self-defense. Friends of the shooter believe he was defending himself.