NORMAN, Oklahoma - Nathaniel 'Nathan' Ewing, 20, was shot and killed during an apparent robbery on Sunday night, according to Norman police.

Police were called just before 11 p.m. Sunday to the Willow Brook Apartments near Lindsey and 24th Avenue SE.

At the scene, officers found Ewing with a gunshot wound to the stomach.

Ewing was taken to an area hospital where he died Monday morning -- his 20th birthday.

"No one ever expects something like this to happen," Nick Whitten said Ewing was one of his best friends. "I love the guy ... he's like my brother."

The family-like bond the two shared has motivated Whitten to put some of his grief aside in an effort to be there for Ewing's family.

"It is rough ... not just for me though. You gotta get your thoughts on the family because they need more help than anyone right now," said Whitten.

Norman police said Ewing and another individual were contacted by two men in the parking lot of the apartment complex.

Witnesses told police the men tried to rob Ewing and the other individual.

During the incident, two shots were fired. Ewing was hit once. The other individual ran from the scene and was not injured.

The two men drove away from the scene in a light-colored sports utility vehicle.

Ewing did not live at this location and it remains unclear why he was at the apartment complex that night.

"I'm not focused on that. It is not going to change what's happened to him," Whitten explained. "If they get the guys, if they don’t get the guys, it is not going to bring my friend back."

The two became friends while enrolled at the University of Oklahoma.

Ewing was an OU sophomore who was studying to be a pilot.

He'd also recently adopted a puppy.

The puppy, a black and white Labrador mix, has been missing since the night of the shooting.

"The family really wants to get a hold of the puppy," Whitten said. The puppy was with Ewing when he was shot and killed.

The family is hopeful someone will return him so they can have something of their son's to hold on to.