Ann Anastasi and Gabriel Struss (Anne Arundel County Police)

The Anne Arundel County woman called police last week to say that her husband had taken his life inside their home after killing the 25-year-old woman who lived in their basement, a prosecutor said. They had argued.

The scene seemingly fit Ann Anastasi’s carefully crafted story: Anthony J. Anastasi Jr., 40, was found dead in the master bedroom with a gun next to his body, charging documents show. Jacqueline Riggs was discovered dead in the basement with stab wounds.

But as investigators probed deeper, inconsistencies mounted and evidence pointed to something far more bizarre having transpired inside the brick colonial in Lothian, Md. Prosecutors said the 42-year-old wife had meticulously staged a murder-suicide.

On Friday, they said that Ann Anastasi enlisted a 13-year-old girl to plan a murder and recruited the girl’s 18-year-old boyfriend to carry it out. Prosecutors contend that a love triangle involving both of the Anastasis and Riggs had gone wrong.

Police announced that they had charged Ann Anastasi; the boyfriend, Gabriel Struss of Annapolis; and the 13-year-old girl in the case. The Washington Post generally does not identify juveniles charged with crimes. Anastasi was held without bond Friday after a brief hearing in Anne Arundel County District Court.

“What we have is a fairly unique situation or fairly rare situation that a mother and two young people are involved in the killing of a spouse,” Wes Adams, the Anne Arundel County state’s attorney, said at a news conference.

Adams said Ann Anastasi — a mother of five, ages 8 to 17 — was “instrumental” in covering up the crime, even swapping out the real murder weapon for a fake one. He said it was troubling that she involved two young people and was a danger to her own children.

She has no history of criminal behavior, drug abuse or mental health issues and has worked as a personal assistant for years, her attorney said.

Police were first alerted to the incident about 1 p.m. Oct. 5, when Ann Anastasi called 911 to say her husband had committed suicide, according to charging documents. Officers found Anthony Anastasi dead. He had been shot in the head.

Ann Anastasi told the officers that she, her husband and Riggs had been drinking the night before and searching the Web for a new vehicle for Riggs, according to the documents. Her husband, she said, later went to the basement with Riggs, and Ann Anastasi said she heard them arguing.

Ann Anastasi told the officers that her husband came back upstairs and told her to not go into the basement or bother Riggs, the documents state. She told investigators that he instructed her to grab their pet kittens and leave the bedroom. He then locked the door.

The next morning, Ann Anastasi told officers, she awoke to tend to the children, the documents state, and took one to the dentist. She later stopped at a grocery store.

When she arrived home, she decided to wake her husband but couldn’t, she told police. She saw the gun and called 911, she said.

Officers found Riggs’s body in the basement.

Investigators began to question Ann Anastasi and found her statements “inconsistent and misleading,” according to court documents.

Adams, the prosecutor, said that Ann Anastasi allegedly placed a .45-caliber gun next to her husband’s body but that it was a .38-caliber bullet that “inflicted the fatal wound.” A murder weapon has not been recovered.

Traces of gunshot residue were also found on Ann Anastasi’s clothing, the documents state.

Authorities allege that further investigation began to uncover evidence of a plot.

They said in court papers that on the evening of Oct. 4 and into the next day, Struss had been texting the 13-year-old girl and Ann Anastasi “regarding the killing of two people.” In one text, authorities said, Struss told the girl that if she talked to police, he “would be going to jail for life.”

Struss’s family could not be reached to comment, and court records did not list an attorney for him.

The Anastasis had been married for 18 years, but their marriage was “fraught with conflict and domestic abuse,” according to charging documents. Authorities believe that Riggs had moved into the basement of the Anastasi residence over the summer, “which caused tension.”

The Anastasis and Riggs had previously been involved in a romantic and sexual relationship, according to court papers. But authorities allege that after the marriage had soured, the intimacy between Anthony Anastasi and Riggs continued without Ann Anastasi.

On Friday afternoon, family members and law enforcement officials were gathered inside the house. Three family members reached by The Post declined to comment.

A neighbor, Cindy Hall, said that the family moved into the house about a year ago but that she did not know them.

She said she watched officers in full SWAT gear gather behind an old barn adjacent to her home Thursday night and run through her back yard and the cornfields toward the Anastasis’ house.

“It’s hard to imagine something like this happened here,” she said.

Police arrested Ann Anastasi at her home Thursday evening and charged her with two counts of first-degree murder, two counts of second-degree murder and use of a firearm in the commission of a felony.

The 13-year-old was charged as a juvenile with two counts of first-degree murder and being an accessory after the fact.

Struss was arrested early Friday and faces charges including two counts of first-degree murder, two counts of second-degree murder and two counts of conspiracy to commit first-degree murder.

He is scheduled to have a bond hearing Oct. 19.

Court documents state that in text messages, the 13-year-old girl and Struss discussed her taking the “fall” for him.

Jennifer Jenkins and Luz Lazo contributed to this report.