Ann Marie Anastasi, 44, pleaded guilty to two counts of first-degree murder in December

A woman has been sentenced to 60 years in prison in Maryland after she was convicted of killing her husband and their 25-year-old live-in mistress in a murder plot that was carried out by her teenage daughter's boyfriend.

Ann Marie Anastasi, 44, pleaded guilty to two counts of first-degree murder in December, acknowledging there is sufficient evidence to convict her without admitting guilt.

Her 40-year-old husband, Anthony Anastasi Jr., was shot dead and their mistress, Jacqueline Riggs, was found stabbed to death in the basement of their Lothian home in October 2015.

Police say all three were involved in a sexual relationship until Riggs moved into their home in summer 2015.

Once she moved in, tensions between Anthony and Ann grew worse in the alleged abusive household.

Authorities said Anthony would leave the bedroom he shared with his wife to go and have sex in Riggs' basement bedroom.

Anthony continued the sexual relationship with Riggs and no longer invited Ann to participate, creating more problems between them, police said.

Police say Ann plotted killing of her husband, Anthony Anastasi Jr. and their 25-year-old mistress, Jacqueline Riggs (pictured), with her then-13-year-old daughter and her daughter's 18-year-old boyfriend Gabriel Struss. Anthony and Riggs were found dead in October 2015

Prosecutors say at the time of the killings, Anthony and Riggs were still in a relationship and lived together in the basement of the home, but he and his wife were not in a relationship, CBS Baltimore reported.

Ann plotted to kill Anthony and Riggs with her then-13-year-old daughter and her 18-year-old boyfriend Gabriel Struss, police say.

Text messages and phone calls among the three discussed the plan to kill Anthony and Riggs.

Authorities say Struss killed Anthony and Riggs on Ann's command, CBS Baltimore reported.

Anthony was shot in the head while he was sleeping by Russ, who then stabbed Riggs to death.

Riggs suffered 42 knife wounds, 20 stab wounds and 22 cuts, according to the Capital Gazette.

Assistant State's Attorney Jason Knight called the crime scene 'heinous and vicious.'

Gabriel Struss, 18, pleaded guilty to first-degree murder last year and is currently serving a 60-year prison sentence

Hours after the killings, Ann called 911 and reported that her husband had committed suicide.

When she was told that Riggs was dead as well, she was surprised and then attempted to claim the crime was a murder-suicide, the Capital Gazette reported.

However, investigators found that the gun near Anthony's body did not match the one used to kill him. In addition, Ann was found to have gunshot reside on her clothing and hands.

Ann and Anthony had been married for 18 years.

'Ann Anastasi destroyed multiple lives by coldly planning these murders and manipulating children into executing her vicious plan,' Anne Arundel County State's Attorney Wes Adams said Tuesday.

'Were it not for Mrs. Anastasi at the helm of this scheme, the victims would still be alive today.'

Struss pleaded guilty to first-degree murder last year and is currently serving a 60-year prison sentence.