Blackthorne had a history of violence against his ex-wife Sheila Bellush. In 1987 he was arrested for, and pled guilty to, beating her up.
And Blackthorne doesn't deny that he hit her, but said that it was a one-time occurrence: "I did hit her. It was a very low point for me in my life. I've never denied it. But I struck her once, and that's all I ever struck her."
Soon after that, Sheila Bellush filed to end their five-year marriage. It was an ugly, litigious divorce.
In the years following the divorce, police were called to Blackthorne's house many times to mediate family disturbances. Bellush even had Blackthorne arrested for sexually abusing their daughter Stevie, a charge he denies. The charges were eventually dropped.
In the middle of all this turmoil, Sheila met Jamie Bellush. Soon after, they were married. Then, Sheila Bellush won custody of the couple's two daughters, and Blackthorne agreed to have nothing to do with his daughters' lives ever again.
"She beat him," said Kerry, Sheila Bellush's sister. "She took him back to court because she wanted to get on with her life and get away from him."
Jamie Bellush accepted a job promotion in Sarasota, Fla., 1,200 miles away from San Antonio, and the couple and their six children - including the quadruplets - moved there.
Soon after the Bellushes moved, Blackthorne hired private investigator Chuck Chambers to find Sheila Bellush. After some digging, Chambers located her and gave the information to Blackthorne, Chambers said. Three weeks later, Bellush was dead.
Around the same time that Chambers tracked down Sheila Bellush, Danny Rocha got her address. Rocha said Blackthorne gave it to him.
Blackthorne denied this and said he has no idea how Rocha received the address.
When he found out about the murder, Chambers was shocked. "I saw the murder in the newspaper," he said. "And it was like ice water started to run through my veins, because I'm sitting there putting two and two together, knowing how hard this woman was to find."
Even Blackthorne's own relatives suspected he may have been involved. His aunt and uncle Debby and Tom Oliver had raised young Allen Blackthorne for a couple of years when he was a teen-ager.
When Blackthorne visited them 10 days before the murder, he was angry at his ex-wife, upset that he had lost the custody fight, they said. "Allen can't lose," said Tom Oliver. "Allen does not lose. Allen wins."
Investigators felt they had reason to be suspicious. On the day of the murder, Blackthorne was playing golf just outside San Antonio with Rocha, who allegedly organized the murder plot and paid Del Toro to kill Sheila Bellush. Rocha and Blackthorne often plyed golf together.
They gambled, too, sometimes as much as $7,000 a hole.
Denying he had anything to do with his ex-wife's murder, Blackthorne had not been charged with a crime. He refused to cooperate with investigators but he did agree to speak with 48 Hours, provided the news program would review information gathered by Blackthorne and his attorneys.
Blackthorne maintained that he was completely innocent. "I had nothing to do with the death of Sheila Bellush," he said. He called Rocha a "liar."
So then how would Rocha, who didn't know Sheila Bellush, have organized her murder?
Blackthorne said he has no idea.
The legal team for Blackthorne put forth a different murder theory. They claimed to have "compelling" evidence that Jamie Bellush may have been involved in his wife's murder.
Blackthorne's lawyers said that Jamie Bellush told police that at 11:30 on the morning of the murder he was at a doctor's office in Fort Myers, Florida, about an hour and a half's drive from Sarasota. Blackthorne's attorneys said that the alibi didn't check out. A receptionist told the defense that she remembered Jamie Bellush being there a week or 10 days earlier.
Jamie Bellush said that he has "no doubt" that he was at the doctor's office. But he never was able to prove that claim.
Blackthorne also said that Jamie Bellush had a violent side. Police were called to the Bellush house in Texas, after Jamie Bellush allegedly beat Stevie with a belt and a spoon. Jamie Belush was not arrested. The neighbor who called the police said both Jamie and Sheila Bellush abused their kids.
Jamie Bellush admitted to spanking the children but said he doesn't remember if he ever used a belt or a spoon or if he ever had bruised them.
Blackthorne's attorneys also claimed that at the time of Sheila Bellush's death, Jamie Bellush had three life insurance policies taken out on her.
Jamie Bellush said that this is true, but that the policies were taken out years before the murder. The money, he says, has been invested for his kids' education.
But Sarasota prosecutor Henry Lee said Jamie Bellush has never been, and never will be, a suspect in his wife's murder. "Jamie has always been cooperative, as opposed to Allen, who has always refused to cooperate with investigators," Lee said.
On to A Key Arrest