Six-year-old Lydia Mater and her seven-year-old brother Alec were found shot to death at their father's home in Surprise, Arizona, in a murder-suicide. Their father, Brock Mater, who was undergoing mental health treatment and had been separated from the children's mother amid a divorce, shot both children in the head and then fatally shot himself; a rifle was recovered on his lap. The children had been staying with him since the prior Friday, and their mother called for a welfare check after their school reported an unexcused absence. Police believe the shooting occurred the night of Sunday, May 19, 2024, and the bodies were discovered during a welfare check. DCS had a prior unsubstantiated October 2023 neglect report involving Mater that referenced his mental health crisis, suicidal ideation, and a domestic violence incident between the parents.
Contexts/Conditions
Is there any mention of child drug ingestion or overdose?
Is there any mention of a drowning incident (either intentional or accidental)?
Is there any mention of a firearm incident?
The news article reports "Investigators recovered a rifle on Mater's lap" and that the victims died "from being shot in the head." The fatality reports cite "gunshot wounds" and a "self-inflicted gunshot wound."
Is there any mention of inappropriate supervision (e.g., child wandered off and drowned)?
Is there any mention of inflicted injury? (e.g. slapped, punched, kicked, choked)
The fatality preliminary report states the children were "discovered deceased at their home due to gunshot wounds" and that "their father, Brock Mater, inflicted the injuries to Alec and Lydia." The news article states officers "found Mater and the two children dead from being shot in the head."
Is there any mention of malnutrition, starvation, or dehydration?
Is there any mention of medical neglect?
Is there any mention of a motor vehicle crash or incident?
Is there any mention of a murder-suicide incident?
The news article headline describes a "murder-suicide," and the fatality reports state the father "inflicted the injuries to Alec and Lydia" and was "discovered deceased at the home due to a self-inflicted gunshot wound."
Is there any mention of outdoor elements (including hot car deaths)?
Is there any mention of prenatal substance exposure (including fetal alcohol syndrome or neonatal abstinence syndrome)?
Is there any mention of sexual abuse?
Is there any specific mention of shaken baby or abusive head trauma?
Is there any mention of prolonged abuse or torture (including restraints, captivity)?
Is there any mention of an unsafe sleeping environment?
Individuals Involved
Was an adoptive parent or guardian involved in the death?
Was a biological father involved in the death?
The fatality reports identify the perpetrator as "their father, Brock Mater," who "inflicted the injuries to Alec and Lydia." The news article describes him as the father and "estranged husband" of the mother.
Was a biological mother involved in the death?
Was a day care worker, babysitter, or nanny involved in the death?
Was a female paramour or friend involved in the death (e.g., girlfriend, stepmother)?
Was a foster parent involved in the death?
Was a male paramour or friend involved in the death (e.g., boyfriend, stepfather)?
Was another adult relative involved in the death? (e.g., grandfather, aunt)
Was a sibling involved in the death?
Child Characteristics
Was the child adopted?
The news article references "A woman who claims to be the adoptive grandmother of the two children," which may imply the children were adopted, though the relationship described is the grandmother's and the official reports refer to Brock Mater simply as their "father," leaving the adoption status unclear.
Was the child homeschooled (including "cyberschooling") or taken out of school?
Was the child in foster care at the time of the incident?
Was the child living with relatives at the time of the incident (but not parents)?
Is there any mention of a neurological developmental child disability? (e.g., autism, intellectual disability, nonverbal)
Is there any mention of a physical child disability? (e.g., feeding tube)
Is there any mention of prematurity or low birthweight?
Is there a history of child protection reports prior to death (for this child or siblings)?
Both fatality reports note a prior report: "On October 20, 2023, a report was received alleging neglect to Alec and Lydia by Mr. Mater. The allegations were unsubstantiated." The case was closed November 8, 2023.
Does the child have a history of foster care (but not in care at time of incident)?
Is there a history of a sibling death (separate incident from this death)?
Parent/Caregiver Factors
Was an adult charged or arrested for the child's death?
Is domestic violence by the parent/caregiver referenced?
The press statement notes the October 2023 report included "additional concerns regarding a domestic violence incident between the parents." The news article also frames the case as a "domestic violence situation involving children."
Is there any mention that the death occurred in a temporary shelter or while homeless?
Is an intellectual disability of the parent/caregiver referenced?
Is the mental health of the parent/caregiver referenced?
The news article states Mater "had recently been undergoing mental health treatment" and that officers had previously responded to his home "due to a mental health crisis last October." The press statement notes the 2023 report alleged "the father was experiencing a mental health crisis and expressing suicidal ideations."
Is a history of arrests or criminal charges for the parent/caregiver referenced?
Is substance use by the parent/caregiver referenced?
Notable Details
The summary report describes a systemic review process: "in accordance with A.R.S. § 8-469, cases with prior involvement with the Department within 3 years of the critical incident are reviewed by a multidisciplinary team (MDT)," which assesses opportunities for systemic change and feeds an annual report (next due December 1, 2025). Additionally, the news article highlights this was "the second domestic violence situation involving children in Surprise in only a matter of days," noting a psychologist's view that "there were signs that were missed before the shooting" regarding Mater's mental health.
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