NASHUA, N.H. (AP) – Prosecutors say a Nashua teenager and her Connecticut boyfriend tried to give each other an alibi after the boyfriend stabbed her mother to death.

William Sullivan, 18, of Willimantic was indicted on first-degree murder and murder conspiracy charges last week. He and Nicole Kasinskas, 16, have been in jail since August when Kasinskas’ mother, Jeanne Dominico, was found dead in her home.

He is scheduled to be arraigned Wednesday.

Kasinskas is charged as a juvenile, but prosecutors likely will seek to charge her as an adult.

Prosecutors said the couple tried burning and poisoning Dominico before Sullivan stabbed her. The teenagers told police they killed Dominico because they wanted to live together in Connecticut, but Dominico disapproved of their relationship.

According to police affidavits, Sullivan and Kasinskas said they first tried to set Dominico’s bed on fire and tried to get the house’s oil tank to explode. They also tried putting cold medicine and bleach in Dominico’s half-and-half.

When that didn’t work, they told police they decided Sullivan would beat Dominico with a baseball bat and make it look like a burglary. They said Kasinskas stayed at a convenience store to act as look-out while Sullivan beat and stabbed Dominico.

Kasinskas helped Sullivan dispose of bloody clothes and knives at a golf course in Hollis, according to the indictment.

In an apparent effort to cover up their involvement, Kasinskas called her home and left a voice message saying she and Sullivan would be home late. She also called her mother’s boyfriend, leaving a message asking if he had seen her, the indictment charges.

The two teens also stopped by the house of one of her mother’s best friends before going back to the house where they encountered police.

Both Sullivan and Kasinskas initially gave police an alibi for the time surrounding the murder, the conspiracy charge alleges.

Despite the teens’ efforts to clean up, however, police gathered numerous items from the house and yard as evidence, and police stated in reports filed in Nashua District Court that Sullivan later admitted to the murder.

Kasinskas’ 14-year-old brother was not home at the time of the murder. After a custody dispute in local courts, he went to live with his maternal grandfather in Massachusetts.

AP-ES-10-25-03 1022EDT