Convicted killer Paul Stephen Riggins told two former detectives searching for his long-missing wife's remains that he accidentally pushed her down the stairs during an argument in their Elkridge home, according to newly released police documents.

"The only thing I am guilty of was not calling 911," he said from prison on Oct. 3, days before leading Chuck Jacobs, who is now a lieutenant with the Howard County Police Department, and retired Capt. Greg Marshall to her remains, which he had wrapped in a blue tarp and buried in a wooded area in Anne Arundel County more than a decade ago.

Riggins, 50, is serving a life sentence for the 1996 murder of his wife, Nancy Lee Riggins. But his confession does little to unravel the mystery of her death and still-missing skull - a mystery police cannot pursue because Riggins' lawyer has denied further access to the inmate, according to the homicide file obtained by The Sun through a Public Information Act request.

Nancy Riggins' sister and the attorney who prosecuted the case said they don't believe Stephen Riggins' story.

"The fact of the matter is that, had it been an accident, [Riggins] was fully capable of disclosing that long, long ago, and if forensic evidence supported it, he may have faced less serious charges," former prosecutor I. Matthew Campbell said.

Two months ago, Jacobs and Marshall bypassed formal channels and directly offered Riggins a deal. In exchange for leading them to his wife's remains and a detailed accounting of the crime, they agreed to testify at Riggins' parole hearing in 2016.

After she learned of the discovery of the remains, Senior Assistant State's Attorney Mary Murphy contacted Riggins' attorney, who prohibited further interviews with the convicted killer, police records said.

"Honestly, what I wanted to do, I wanted to go back to speak to him at length about what happened to ferret out more details," said Marshall, who retired in January and now works for the U.S. Department of Homeland Security. "They never materialized because of everything that went on. ... It's hard to tell whether he's telling the truth without asking him more questions."

Jacobs has declined to be interviewed. His actions are the focus of an internal affairs investigation.

Prosecutors won a first-degree murder conviction and life sentence for Riggins in 2001, despite the lack of blood or other forensic evidence to explain how Nancy Riggins died. Campbell said that detectives during a five-year investigation found no evidence that Nancy Riggins tumbled down the stairs. X-rays of her remains revealed no evidence of injury, according to police records.

Denise Keenan, Nancy's sister, said that she believes Stephen Riggins is withholding the location of her sister's skull, which could provide clues to what caused her death.

"There's still a question of where her skull is, and he's trying to remain in control of the situation by not telling us the rest of the story," said Keenan, whose family held a memorial service for Nancy Riggins last weekend. "It's probably as much [information] as we'll ever get, because no one's allowed in [the prison] anymore."

According to Riggins' Oct. 3 statement to the former detectives, he returned home from work at the Patapsco Waste Water Treatment Plant on the morning of July 2, 1996. His wife was awake, and they began arguing at the top of the stairs. After "accidentally" pushing her down the steps, he sat on the stairs "for some time just staring at her." He told the detectives that he thought her neck was broken. He then retrieved a blue tarp and carried her to the trunk of their minivan, according to police records.

He drove their daughter Amanda to day care and returned home, stopping to speak to his neighbor. He then drove his wife's body to the wooded area 10 to 15 minutes away in Hanover and dug a shallow grave. He did not bury her until five days later. By then, Riggins said, her body had significantly decomposed and, as he dragged her to the grave, her head became detached.

Dr. David Fowler, Maryland's chief medical examiner and a witness at Riggins' trial, said Nov. 13 that decomposition is most rapid during the summer and that this portion of his confession is plausible.

"It has always been said that in Louisiana - in the heat and swamps, with animal activity - you can have a complete skeleton in three days," he said. "In Maryland, it normally takes a bit longer. ... But in July, you'd expect to find maximum rates of decomposition due to the heat, maximum insect activity and other animal activity on the body."

Jacobs and Marshall sought the location of the remains from Riggins months after negotiations between prosecutors and Riggins' public defender Norman Handwerger failed. Handwerger was seeking a reduced 30-year prison sentence in exchange for the remains - an offer State's Attorney Timothy J. McCrone rejected.

McCrone, Jacobs, Marshall and Nancy Riggins' relatives then agreed on a counteroffer: the officers would appear at Riggins' parole hearing in exchange for the remains and a confession. After months passed, Jacobs and Marshall "both wondered if the counteroffer ever reached Mr. Riggins," according to the police report. "At one point, a decision was made to meet Riggins at the Department of Corrections in Jessup."

At the meeting, Riggins said that he never received the counteroffer, according to the report, and wanted to "do the right thing" because "he has to meet his maker one day." His wife's death had been "weighing on his mind ever since it happened," and he wanted to give her family and their daughter "some peace," according to the report.

Even if Nancy Riggins' skull were found and offered no clues, both Campbell and Keenan said the murder was not an accident, and that Stephen Riggins is not to be trusted. He had been having a four-year affair with the couple's teenage baby sitter. At the time of Nancy's death, she had threatened to tell the sitter's mother and had scheduled a meeting with a divorce attorney.

An inmate said that Riggins told him his wife had left him to join a biker gang in California. He reportedly told yet another inmate that he dumped her body into Curtis Bay.

"You can't believe him," Keenan said. "He told all kinds of stories. Nancy had run off with a biker? It was some of the most outrageous stuff I've ever heard."

melissa.harris@baltsun.com