A man accused of gunning down two Wal-Mart (search) employees in a store parking lot — reloading and continuing to fire into the men after they fell — didn't appear to know either victim and had no known vendetta against the company, authorities said.

Court papers released Wednesday indicated the suspect, Ed Liu (search), 53, was mentally disturbed but gave no further details.

The two employees had been collecting shopping carts in the crowded parking lot of their suburban Phoenix store Tuesday afternoon when a man drove up and started shooting, according to authorities.

Anthony Spangler, 18, and Patrick Graham, 36, were wearing their blue Wal-Mart vests when they were hit. Both died from their wounds.

"This man, in cold blood, gunned down this young man. I mean, it's terrible," said Spangler's grandmother, Norma Blaylock.

Graham's wife, Anita, said police told her the shooting appeared to be random.

"I want there to be a reason. I don't know why, but to me it seems like there has to be," she said Wednesday.

Court documents released after Liu's initial court appearance Wednesday alleged that after shooting the two, Liu reloaded his .40-caliber handgun and then shot them several more times as they lay on the ground about 75 yards from the store entrance.

Two witnesses gave police the license number of the shooter's car, and Liu was arrested a few hours later in a nearby retirement community where he lived.

He was booked late Tuesday on two counts of first-degree murder.

Liu did not immediately respond Wednesday to a request through jail officials for an interview. A search of criminal record databases turned up no criminal history for him in Arizona.

Neighbors said they rarely saw Liu, who had lived in the neighborhood for about seven years.

"He was just a quiet guy and one of those people you would least suspect," said neighbor Judy Devlin.

A Glendale police spokesman, Officer Mike Pena, declined to comment on why investigators believe Liu is mentally disturbed, saying he didn't want to jeopardize the case. He said authorities don't believe Liu knew the victims or held a grudge against Wal-Mart.

Outside the store Wednesday, employees built a memorial of flowers and candles to honor the victims.

"You'll be missed and forever in our hearts," read an inscription on one poster.

Graham and Spangler had worked at the store only since the first week of August, said Delia Garcia, a Wal-Mart spokeswoman.

"Everyone's been deeply affected by the loss," she said.

Graham and his wife had two sons and would have celebrated their 11th anniversary next month. Anita Graham said her husband worked two jobs to support the family.

"He'd always go out of his way to help anybody," she said.

Spangler graduated from high school in June and had gotten the Wal-Mart job to save for college, said Blaylock, who had raised him. He wanted to become an archaeologist.

"He was very, very kindhearted," she said. "I just wish he was here. I want to see that smile."

The store, about 20 miles northwest of downtown Phoenix, closed after the shooting but reopened Wednesday morning.