Police were investigating a fatal shooting that took place in the parking lot of a north-side smoke shop around 1 p.m. Sunday.

When police arrived at Sky Smoke Shop, 247 W. Grant Road, near North Oracle Road, they found Dereck Castro, 21 with gunshot injuries, said Sgt. Diana Lopez, a Tucson Police Department spokeswoman. He was pronounced dead at the scene.

Lopez said it appears that Castro and another man got into an argument that escalated to the shooting.

Mhoamed Ben, an employee at the smoke shop, said he was helping a customer and didn't hear the fight. Ben said he did hear the gunshots, however, and went outside afterward. He said he tried talking to the victim, but got no response and then called 911.

"The guy was bleeding. He was shaking," he said.

Ben said he heard a vehicle leaving after the shooting, but didn't get a good look at it because he was still inside.

Police said a truck was seen leaving the scene after the shooting. It was found a block or so away, but the driver was gone, police said.

Lopez said homicide officers were on the scene and unsuccessfully searched the area with dogs late Sunday.

They said the motive for the shooting was unknown.

Ben, who has worked at the smoke shop for about four months, said he has never seen or heard of fights near the business before.

"We don't have any problems," Ben said.

Contact reporter Marisa Gerber at mgerber@azstarnet.com or at 573-4142.