San Diego — May 17, 2006, San Diego Police homicide detective Robert Donaldson was thumbing through cold-case files looking for something that might warrant reopening an investigation: a bit of physical evidence, blood maybe, that modern forensics could use to identify the killer in a decades-old murder case. At about 11:30 a.m., the phone rang. On the other end, Donaldson recalls, was "a guy that identified himself as Peter Jacob Johnson, and he told me that he had information on a homicide case that occurred sometime in 1978, 1979, or 1980. He asked me if the case was still open. I told him that until he provided me with additional information, I would be unable to tell him. And Johnson then told me that he remembered that the victim was a white male, around 20 years old, and his first name was Robert."

It was all pretty vague, and Donaldson says, "I was kind of skeptical. Here's this guy, what is he fishing for? I didn't understand what this guy was really up to. Then Mr. Johnson says, 'The victim had been shot in the head, and he was found in the trunk of his car in the Kearny Mesa area of San Diego.' Then he goes on to describe the car, which this guy Robert was found in, as a mid- or late-'60s model, but he didn't know the make or model."

That got Donaldson's attention. "Then Mr. Johnson asked me again if the case were still open. Well, I told him, I didn't know, that particular case didn't ring a bell, and I told him that I would have to do some research on the case and get back to him. And Johnson stated that he lived in Oklahoma City, and then he gave me his cell phone number. He didn't want to tell me his home address, but he said I could always call him back on his cell phone."

Donaldson took the information Johnson had given him and dug into the unsolved murder cases from 1978, 1979, and 1980. "I think it was two days later," he recalls, "at about 9:30 in the morning, I am in the office when I get a call, and I remember the voice of Peter Johnson. He asked me if I had located the case he had told me about in our telephone conversation a couple of days ago. And I said, 'I am still looking into it, still working on it.' And then Johnson tells me just out of the blue, 'I did it. I shot him in the back of the head, behind the right ear, with a .38 handgun.' Then he says, 'The body was found in an alley off of Murray Ridge Road.' "

Gone was any skepticism Donaldson harbored toward Johnson. "Now I knew," he says, "this was a suspect. I mean, no one would know these details."

Turns out, Donaldson had already pulled the case Johnson described in their first conversation. It was sitting on his desk when Johnson called the second time. Donaldson flipped it open and saw that the victim, Robert Spencer, "was age 19, which fit Mr. Johnson's description. The date of the case was September 17, 1978, the day Spencer's body was found in the trunk of a vehicle at 2900 Murray Ridge Road in the alley," all of which fit Johnson's description but all of which was published in San Diego Union reports on September 18 and 19 of 1978. What wasn't in the Union reports, but was in the case file, was the caliber of the weapon -- .38 -- and the fact that Spencer had been shot behind the right ear. Also in the case file was an interview police had conducted in the days following the murder. The subject: Peter Jacob Johnson. Police had talked to Johnson the day the body was found because he was known to be a friend of Spencer's. According to court documents, Johnson told police that "he thought he had met Spencer about two or three weeks before, and [he] knew that Spencer lived in the apartment below him. Johnson admitted that he had been with Spencer on Friday night, September 15, 1978. Spencer had come up to Johnson's apartment where they drank a beer or two, and then Spencer had left."

The interview and other police work didn't produce enough evidence to charge Johnson with the murder. Nearly two years later, police received a message from Idaho that offered a possible explanation for the unsolved murder case. "In May 1980," court documents state, "SDPD received a teletype from the Boise Idaho Police Department. The teletype advised that a Donald Allen Young, who was currently in custody for a shotgun homicide in Boise, had also been fingered by an anonymous and unconfirmed source as a participant in one or more homicides in California during the months of September and October 1978. One of these incidents involved the death of a young male adult whose body was allegedly located in the trunk of a vehicle in San Diego. Based on this teletype, SDPD detectives investigated Donald Young as a suspect in the murder of Robert Spencer. Detectives developed information that Donald Young and the victim Robert Spencer had been acquainted with each other, had attended the same high school [in Idaho], and had worked together. However, the detectives were unable to develop any actual evidence (beyond mere suspicion) that Young had murdered Spencer, and they never interviewed Young as a suspect."

Donaldson kept Johnson talking during that second phone conversation. And Johnson told the detective that he had "used a lot of drugs in those days" and he'd done drugs with Spencer on a few occasions. Despite being 13 years younger, Johnson told Donaldson, "Spencer was a kind of friend [of Johnson's]. He knew him in the drug world."

Johnson, Donaldson says, continued "volunteering details about the shooting. He said they were going to a local bar right around the corner from where they were living. 'I am in the back seat, the victim was driving in the front seat. I had him pull over to the side of the road.' Then Johnson confronts him, Spencer, as being a child molester. And all of a sudden Johnson just shoots him one time. And then Johnson gets in the driver's seat, drives to the alley, and then puts Spencer into the trunk. It sounds like Johnson lured Spencer into the car so he could do this. It was an execution."

No one knows if Johnson's contention that Spencer was a child molester is true or not. Donaldson says Spencer was never accused or convicted of molestation either in San Diego or Idaho.

Donaldson asked Johnson why he had decided to unburden himself 28 years later. "He basically told me that he had been out in Oklahoma for about 6 years, and he said he was involved with a woman out there and he wanted to come clean for this woman. But we went out there, and we interviewed a lot of people and couldn't find anybody that said he was involved with a woman. So I don't know if that was another reason or he just said that. But I think he just wanted to clear his conscience. And I really believe that he was just tired. He was basically homeless, he had no job, had no money as far as we could tell. He was homeless, and that was his motivation. He didn't say that, but I believe that was his motivation. He just had nowhere else to go. He thought that, because it happened in 1978, he would get maybe five years in prison, and when he came out he would be 65 and eligible for Social Security."

He thought wrong. Sentencing guidelines at the time of the murder called for a life sentence. On May 24, 2006, Donaldson flew to Oklahoma City with another detective and arrested Johnson. "He knew it was coming," Donaldson says. "He had sold and given away what little he had, and he signed his car over to a friend. He knew he was going with us. There was no surprise."

What was a surprise, at least to Donaldson, was the fact that Johnson took the case to trial instead of striking a plea bargain with the district attorney's office. Another surprise was that on November 29, 2006, Johnson testified on his own behalf, against his public defender's advice. Once on the stand, Johnson denied murdering Spencer. "He said," recalls deputy district attorney Jeff Dusek, "that he was down on his luck in Oklahoma, didn't have any money, didn't have any place to stay, was living out of his car. So he decided that he had to confess to this first-degree execution murder so he could have a place to stay for maybe three years or so. And California would house him and feed him, and the federal government would give him Social Security while he was in jail. So he would have some money when he got out after three or four years."

Though there were other witnesses for the prosecution who corroborated the fact that Johnson knew Spencer, Johnson ended up being chief witness for both the prosecution and the defense. Jurors had to decide whether he was telling the truth on the stand or during his tape-recorded conversations with Donaldson. "Yes," says his public defender, John Thomas, "it came down to that. And a lot of facts that came out in his phone calls were damaging to say the least."

On November 30, Peter Jacob Johnson was found guilty of first-degree murder. He was sentenced January 20, according to 1978 guidelines, to life with the possibility of parole. Thomas says he won't be eligible for parole until 2014. But he says, "Normally, you don't get parole the first time your name comes up. But he has some health issues. And the prison system has a tendency to overlook precedent and kick people out when they are sick, because it's expensive as hell to keep them in."