As the city shuttered itself in fear of serial killers this summer, Ron Horton found himself having an odd conversation with an old drinking buddy.

"Let me ask you something," Horton remembers his friend, Samuel John Dieteman, sliding over to tell him between beers in June. "Do you know what it's like to kill a man?"

"How would I know?"

"Well," Horton recalls Dieteman saying, "neither did I until the last few months."

In an exclusive interview with The Associated Press, Horton said Dieteman went on to describe how he and a friend poked shotguns out car windows and blasted at people as they cruised by.

"They called it 'RV'ing,"' Horton said. "Random Recreational Violence."

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Horton initially thought it was just a false barroom brag from a man he thought he knew well, a former roommate who liked joking and drinking and who twice punched out men who were being rough on their girlfriends.

He would come to regret not believing it sooner.

Horton led police to Dieteman, 31, and Dale Hausner, 33, who were charged this summer with slayings attributed to the so-called Serial Shooter. Police say seven people were killed and 17 wounded in the random attacks across the area dating to May 2005, which mostly came as the victims walked or bicycled alone late at night or in the early morning.

Horton's role as an informant was confirmed through a nonpolice source with access to documents from the investigation who spoke on condition of anonymity because the information has been sealed.

Police spokesman Sgt. Andy Hill said help from the public was critical to solving the case, but he couldn't comment specifically on anyone's involvement. Dieteman, who is jailed, has not responded to repeated interview requests made through authorities.

Horton, a soft-spoken 48-year-old with a shaggy blond mane, still shakes his head when thinking about his conversation with Dieteman at the Rib Shop, a west Phoenix bar. He said he thought Dieteman was lying, that he was incapable of the cold-hearted acts he described.

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Horton's suspicions grew in July, when he says Dieteman sent him a text message saying he was angry and that somebody was going to get hurt.

He went to police later that month, after hearing from a friend in his pool league about the Serial Shooter, blamed at that point for five slayings and the deaths of several dogs and horses.

No one had been killed since Dieteman's conversation with Horton but several people had been wounded — a 19-year-old shot while pushing his bicycle, a woman shot in the back of the head while walking.

Finding Dieteman was a problem, Horton said. His living situation changed frequently — he lived with Horton in fall 2005 — and he had just changed his cell phone number.

Horton finally found Dieteman's new number through a friend and started text messaging him July 30.

Dieteman was slow to answer. When he did, he only left short, vague responses. Horton tried again: "Hey, if you're busy, call me when you're not busy," and he waited.

That night, 22-year-old Robin Blasnek was shot to death while walking along a street in Mesa. The news crushed Horton, who called police and promised to be more aggressive.

"It affected me quite a bit," Horton said. "I wasn't sure if I could have done something earlier."

Horton kept text messaging Dieteman, who finally agreed to meet at the Stardust bar in Glendale.

Undercover officers watched as Horton drove Dieteman to another bar, then to a casino on the Gila River Indian Reservation. It was getting late, and Horton asked Dieteman to get a ride home from Hausner, Dieteman's roommate at the time.

He left his old friend at the casino, eating a club sandwich. Dieteman and Hausner were arrested two days later, on Aug. 3.

Dieteman has been charged with two counts of murder — Blasnek's slaying and May 2 shooting of Claudia Gutierrez-Cruz — and Hausner is charged with seven counts of murder. Both have pleaded not guilty.

One 2005 fatal shooting was connected to the Serial Shooter case after Dieteman and Hausner were arrested.

According to police documents, Dieteman admitted to some of the crimes, saying Hausner came up with the idea. Hausner has denied involvement and has suggested that Dieteman had taken Hausner's guns and car while he was asleep.

The county attorney plans to seek the death penalty.

Horton said it wasn't easy giving up a friend, but he'd do it again.

"He let us all down," Horton said.

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