Keller said tips generated by release of security camera images of a silver Chevrolet Sonic hatchback with a sunroof in the area of the April 16 slaying had proved critical to closing the case.
Holt's family offered a $10,000 reward for information leading to an arrest.
Earl Holt, the victim's father, said he was pleased an arrest had been made, but he knows the family still must endure court appearances and a sentencing before closure can occur.
"I'm glad this part of it is done," he said in a phone interview. "My wife and I both don't want any vengeance, but we're happy there's been an arrest.
"It's just a senseless thing that happened to our son. He was such a good man, and he touched so many lives."
Holt added his appreciation for South Salt Lake police: "They have worked on this so hard. They have been very good to us."
About 10 p.m. Sunday, an off-duty South Salt Lake police officer spotted the Sonic at a home near Quebec Circle in Tooele. Joined by Tooele city officers and Tooele County sheriff's deputies, the officer contacted the registered owner of the car Shepherd.
A probable cause statement accompanying Shepherd's Salt Lake County jail booking stated that after waiving his Miranda rights, Shepherd confessed that he had approached Holt and demanded cash at gunpoint.
Despite receiving money, Shepherd, according to the booking statement, shot Holt anyway, then picked up his shell casing and drove away from the scene, near the Jordan River Parkway.
Police say Shepherd also admitted to disposing of his handgun, the casings and clothing, and washing blood away that had sprayed onto his car.
Holt was shot inside his car while parked in a lot at 3200 South and 900 West. A passer-by found the car, driver's side door open, and Holt's body inside early Easter Sunday morning.
Why Holt was in the parking lot remained a mystery as of Monday. Keller said the case remained under investigation.
Shepherd had not been formally charged as of Monday afternoon.