A gunman in a van in a Wal-Mart parking lot killed one police officer and critically wounded another Friday, prompting an hours-long standoff that trapped customers in the store for hours before the attacker was found dead.

Sgt. Gregory Hunter (search), 54, was fatally shot Friday morning as he and another officer, Bruce Seix, checked on a blue camper-style van that had been parked all night with its engine running, said police spokesman John Brimmer.

Hunter went to the front of the van and Seix to the side, Brimmer said. The suspect, whose name was not released, shot Hunter at least twice through the front windshield; Seix managed to fire a few rounds before he was wounded.

John Jacobs, the manager of a Payless ShoeSource near the Wal-Mart, heard three pops, then another volley of pops.

"When I heard whistling, I knew rounds were coming in our direction. ... I hit the ground and I called the cops," said Jacobs, who was locked alone in the store during part of the standoff.

Seix, 44, was hospitalized in critical condition after his lung and liver were pierced by bullet fragments, but was "conscious and talking," Brimmer said.

SWAT team (search) spent the day trying to negotiate with the man, but he never responded. Brimmer said the man apparently used his cell phone at some point to call his girlfriend.

About five hours after the shooting, SWAT officers shot several flash-bang grenades and tear gas into the van.

When officers entered, they found the man dead inside. Brimmer said he appeared to have been wounded by one of the shots fired by Seix.

For about three hours, 150 Wal-Mart shoppers and 60 employees were locked inside the store as a precaution. Customers said they sat in patio chairs and watched developments on televisions in the electronics department before they were escorted out a back door.

A Wal-Mart employee told The Dallas Morning News the original call asking police to investigate came after an employee heard a strange noise from inside the van. Brimmer said the vehicle was reported stolen in New Mexico in February.

Hunter became the Grand Prairie Police Department's (search) first black officer when he was hired in 1973. He left briefly for a security guard job, then returned to the force in 1983. He became a sergeant five years ago, Brimmer said.

Seix has been a police officer since April 1995.

Grand Prairie is a suburb between Dallas and Fort Worth.