Officers believe a man beat his 14-year-old stepbrother to death as the mother of the boy watched and then walked away.

Rebecca Greenwood, 52, and David Matheny, 33, have been charged with murder after 14-year-old Sayeed Nelson was found dead at their home in Nashville, Tennessee, Friday.

Police say Greenwood called 911 saying that Nelson, her son who has autism, appeared to be dead. She and Matheny reportedly told officers that Nelson fell in the shower and hit his head on Thursday night. Greenwood then said she and Matheny checked on the boy multiple times that day, then went to a bar for drinks and checked on him again before going to bed that night.

Greenwood and Matheny told police they bought cleaning products in the morning and returned home to the boy unresponsive in his room.

Nelson’s injuries were inconsistent with a fall and when taken to the police department for an interview, Greenwood admitted to seeing Matheny punch and kick the boy in the head.

Police say she told Matheny to stop beating Nelson and then walked away without making sure the attack had ended.

Officers believe the pair bought supplies and cleaned the house to destroy evidence of Nelson’s death.

Greenwood and Matheny are charged with criminal homicide, aggravated child abuse, and evidence tampering.