The man accused of fatally shooting a Colorado horse breeder at an Atlanta gas station claims the incident resulted from a drug deal gone bad, police said.

But the lead investigator on the case told a court Tuesday that James Stewart likely had another motive for killing Douglas Perry.

"I think he was just there to rob Mr. Perry," Atlanta Police homicide Detective Michael Willis said in the hearing. "I think he saw an older, white-haired gentleman who had just filled up a new car ... and tried to rob him."

Around 5 a.m. on July 3, shots were fired inside the rental car Perry was returning to the airport before catching a flight back to Colorado.

Perry lay dying next to his car, and witnesses, many of whom know Stewart, say they saw him run from the BP gas station where Perry was filling up, across Donald Lee Hollowell Parkway to his own vehicle.

Perry was shot three times, including one shot that penetrated his heart and right lung and left the bullet lodged in his spine, Willis testified.

Stewart, 34, was in court Tuesday for the first time since he was arrested for the shooting death of the 62-year-old Perry.

Perry's family members were also in court and reacted with tears as Willis described the incident and Stewart's admission to police.

They declined a request for interviews after the probable cause hearing.

Willis said he spoke with Stewart on the phone while interviewing Stewart's twin brother, Jesse Stewart.

"James called Jesse's phone during the interview," Willis said. "'I had to do it,' he said. 'The man was going to stick me.'"

No video footage of the shooting was available to police from the BP, investigators said.

Inside the car, police found three spent 9 mm bullet casings, a pair of sunglasses, keys to the rental car and Perry's briefcase, authorities said.

When Stewart was arrested, Willis said, he described having been cheated out of money during a drug buy and was paranoid as a result.

"He said Mr. Perry had been out in the area most of the night," Willis said. "He said Mr. Perry came and bought some drugs from him."

Investigators say Stewart admitted to shooting Perry.

"He said he was sitting in Mr. Perry's car and was breaking off a piece of cocaine, when Mr. Perry rushed at him," Willis said, noting that Stewart said he thought Perry had something in his hand.

As public defender Stanley Constant cross-examined Willis, however, the detective pointed to evidence from the crime scene to dispute Stewart's claims.

"I would imagine that if he was breaking up a slab of cocaine and something happened, in the heat of the moment, Mr. Stewart would've dropped the cocaine.

"No evidence of any drugs was found inside the car," Willis said.

Constant continued with his cross-examination.

"Did you find a wallet?" Constant asked.

"No," Willis responded. "Mr. Perry was about to get on a plane, but we found no wallet ... no ID ... nothing that he would need for boarding."

A Delta Air Lines ticket and several Colorado state horse breeding IDs were found in Perry's briefcase, Willis said, but no other identification.

Fulton County Superior Court Judge Karen Smith Woodson said there was sufficient evidence to charge Stewart with one count each of malice murder, felony murder, possession of a firearm during the commission of a felony and possession of a firearm by a convicted felon.

Woodson then denied bond for Stewart after hearing Assistant Fulton County District Attorney Jack Barrs tell the court that the defendant had "six probation or parole violations over the past 10 years."

Stewart will remain in the Fulton County jail while he awaits trial.