UPDATED: Oct. 16, 2015 7:10 p.m.

WASHINGTON — A woman and her 13-year-old daughter recruited the girl’s boyfriend in a plot to help kill her husband and their 25-year-old lover, who lived in the family’s basement, police and a relative said Friday.

The mother and her husband had both been involved with the woman, Jacqueline Riggs, but the couple’s 18-year marriage, which was “fraught with conflict and domestic abuse,” became more strained as the wife fell out of the love triangle, according to charging documents.

The mother and daughter decided to kill Riggs and the girl’s 40-year-old father and recruited the girl’s boyfriend, 18-year-old Gabriel Struss, to help, police said. The woman initially told police her husband committed suicide, but authorities said the cover-up unraveled as investigators learned the evidence didn’t match her story.

Now the 42-year-old mother, her daughter and the boyfriend face first-degree murder charges. The girl is charged as a juvenile. The Associated Press generally does not identify juveniles charged with crimes and is not naming her parents to avoid identifying the girl.

The 13-year-old’s grandfather says she is one of the couple’s five children.

Authorities learned about the deaths when the wife called police Oct. 5 and said her husband had killed himself at their home in Lothian, about 20 miles east of Washington, D.C., according to charging documents. Officers found him in the master bedroom with a gunshot wound to the upper body, police said. He was pronounced dead at the scene.

The wife told police that she, Riggs and her husband had been drinking in their bedroom the night before, and later, her husband and Riggs went to the basement and argued. When he returned, he told her to get out and not to bother Riggs.

She told police that she slept elsewhere. She said she tried to wake him, noticed a handgun next to him and called police.

After learning of Riggs, officers checked the basement. An autopsy showed she had multiple cuts and stab wounds.

Forensic analysis of several pieces of evidence “did not coincide with what the crime scene depicted,” police said. For instance, investigators found a .45-caliber handgun next to the husband’s body, but a .38 shell casing nearby. Analysis of the bullet that killed the husband showed it was not fired from the handgun found next to him, and investigators also could not find a weapon that they believed could have been used to kill Riggs, the charging documents said. There was also no sign of an intruder.

A review of phone records showed the wife, her daughter and Struss discussed the slayings over text message, according to charging documents. In one text, Struss told the girl that she shouldn’t talk to police or he would go to jail for life. In another exchange, the teens discuss the girl taking the fall for Struss.

The mother was arrested Thursday and is being held without bond. In an interview after her arrest, the woman said that she had picked up Struss the night of the slayings and brought him to her home.

Struss, who is also charged with several counts of conspiracy, was arrested in Annapolis early Friday. The 13-year-old girl, who is also charged with accessory after the fact, is being held at a juvenile detention facility.

A person who answered a telephone number for the Struss familiy said they did not have any comment and hung up.

Reached by telephone Friday at his home in Florida, the wife’s father said that he spoke to his daughter several times after the bodies were found and that she “seemed to be doing reasonably well.” He said he had not talked to her since she was arrested.

The woman’s father said his daughter and son-in-law had five children ranging in age from 8 to 17. He said the couple moved to Maryland from Michigan about two years ago, but that he wasn’t in regular contact with them.

He said his daughter had been working as a personal assistant, and his son-in-law was driving a truck. He said it had been 10 to 15 years since he’d last seen his daughter.

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