Family members found the decapitated body of a beloved teacher late Friday after she failed to arrive for a surprise birthday party earlier in the evening.

Teresa DeJesus Cruz Rubio’s sister told investigators she had spoken with her late Friday afternoon to confirm she was coming to the planned gathering, KSAZ reported. When the 49-year-old didn’t arrive, family members went looking for her.

With the help of a locksmith, they got into her house and found the body shortly before midnight.

“The 911 caller stated a family member was inside the house, was deceased, and that the victim’s head had been cut off,” Glendale Police Sgt. Bryan Hoskin said.

Investigators developed Cruz Rubio’s son, 25-year-old Alejandro Gonzalez, as a suspect and set out looking for him. He had been seen in his mother’s car around 5 p.m., police said, and a short while later used his mother’s phone to call family members.

Just after 2:30 a.m. on Saturday, Phoenix Police spotted the car and took Gonzalez to Glendale for questioning.

Police said that Gonzalez admitted stabbing his mother with a kitchen knife and decapitating her, but he reportedly said that another, unknown man stabbed her first and that he killed her so she wouldn’t be in pain, KNXV reported. Police found no evidence of a second person at the home or involved in the murder.

Gonzalez was found with injuries on his hands and arms and bloody clothing and has been charged with first degree murder. He is being held on a $1 million bond, KSAZ said.

Cruz Rubio worked as a teacher at Southwest Key Programs, a nationwide nonprofit that provides services to children and families. Family members said Gonzalez had recently gotten out of jail and was living with his mother.

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[Featured image: Teresa DeJesus Cruz Rubio and Alejandro Gonzalez/handouts]