Prosecutors: Andrew Dykes killed Tanya Jackson, formerly known as a Gilgo Beach victim, after she tried to break up his marriage

Nassau prosecutors said they believe  Andrew Dykes, a former Tennessee state highway patrolman, killed his former girlfriend, whose dismembered body was once tied to the Gilgo Beach serial killer probe, because she tried to break up his marriage, court documents show.

A grand jury indicted Dykes, 67, of Ruskin, Florida, in December on a single count of second-degree murder in the death of Tanya Jackson, 26, a Gulf War veteran with whom he had an extramarital affair while they were both in the Army.

Jackson’s partial remains were discovered stuffed in a Rubbermaid container on June 28, 1997, in Hempstead Lake State Park.

He has not been charged with the death of the child that they had together, Tatiana Dykes, 2, whose body was found in Jones Beach State Park in 2011, along with more remains of Jackson.

Prosecutors revealed the theory of Dykes' alleged motive in their motion opposing the defense attorney's August request to dismiss the case due to violations of his client's rights and an insufficient grand jury presentation. They also argued in court papers that police did nothing wrong in secretly recording Dykes during an interview.

For decades, detectives believed she could have been another victim of the Gilgo Beach serial killer. They identified her as Jane Doe No. 3 or "Peaches" for the heart-shaped tattoo of a peach on her body. Investigators identified both the mother and baby in 2023 through genetic testing. Dykes’ name appears on the child’s birth certificate as the father. DNA evidence found on a vaginal swab taken from Jackson matched the Florida man.

Dykes has pleaded not guilty and has remained in Nassau County jail since his arraignment last year.

Jackson met Dykes in the military in the mid-1990s when she was a medical technician and he was an anatomy and physiology instructor at Fort Sam Houston in  San Antonio.

Dykes was married with children at the time, his son, Aundrey Dykes, previously told Newsday. The Army later transferred him to Fort Hamilton in  Brooklyn, where he finished his military career.

Jackson’s acquaintance Tammy Coleman testified before a Nassau County grand jury that her friend felt "hostility" toward Dykes’ wife and she "would often seek out [his] wife to confront her about the relationship," according to prosecutor Ania Pulaski’s brief.

"Ms. Jackson did so in the hopes that [Dykes] would leave his wife for her," the prosecutor wrote in court papers, paraphrasing Coleman’s testimony.

The friend said Jackson was so determined to be with Dykes, court filings show, that the moment she got out of the hospital after giving birth to their daughter in Texas, she "packed her bags and drove herself and her baby to follow [him] to New York, where he was stationed and living with his family at the time."

Aundrey Dykes, 43, of Orlando, Florida, said Coleman’s recollection did not square with his memory growing up. He recalled only one time that Jackson called the house to speak with his mother.

"My mother is the most God-fearing woman, and she would never argue with anyone over my dad," he said in a phone conversation with Newsday. "I remember her saying, ‘ “If you want him you can have him’; she was not about to fight over him."

Pulaski argued Coleman’s statements show Jackson’s state of mind regarding Dykes and his wife "and are further relevant in considering his potential motive."

After Jackson’s disappearance, Dykes never reported it to the police, prosecutors said, he told investigators he believed she had left on her own.

Another grand jury witness, identified only as TH in court papers, testified Jackson told her in June 1997, the same month Jackson's body was found, she would be staying in New York and bringing her sister up from Alabama to live with her.

In August, defense attorney Joseph LoPiccolo asked state Supreme Court Justice Tammy Robbins to dismiss the case over a violation of Florida privacy laws during a recorded interview with Nassau County investigators. The defense lawyer argued because Florida law requires all parties to consent during a conversation, and his client was unaware he was being recorded, the detectives violated his client’s rights.

Pulaski countered in court papers filed last week that there is a carve-out in Florida law for law enforcement officers conducting an interview as part of an investigation. She cited case law that allowed an undercover officer to record a conversation without skirting the law.

LoPiccolo pointed out the exception applies only to Florida law enforcement, not Nassau police.

The younger Dykes said he was not worried about his father’s statements to police.

"At the end of the day, there’s nothing that he said that was untrue," Aundrey Dykes said.

Nassau County prosecutors also said in court papers that they intend to introduce Dykes’ disciplinary history as a state trooper into the trial testimony.

Pulaski said Dykes had been fired from the Tennessee Highway Patrol.

Dykes spent eight years working security with the Tennessee Department of Labor after he left the state police, according to personnel records.

Prosecutors intend to file additional arguments later this week.

The judge’s decision on the defense motion to dismiss is expected toward the end of November.