LAS VEGAS (FOX5) -- After months of investigation, the Clark County coroner released the cause and manner of death for 3-year-old Daniel Theriot on Thursday.
According to the coroner, Theriot died due to blunt force trauma. His manner of death was determined to be homicide.
On Sept. 2, 2018, Theriot's mother, Cassie Smith, 20, reported him missing at around 9 a.m. near Sunset Park. Smith claimed she was at the park with her son to feed the ducks when she took a phone call, and had her back turned towards her son. When she turned around, Smith said Theriot was gone.
The call led to a frantic search that lasted for approximately 12 hours. Multiple law enforcement agencies responded to the call, including Red Rock Search and Rescue, Clark County Park police, Child Protective Services, FBI Child Abduction and Rapid Deployment team and the National Park Service.
At around 1 p.m. on Sept. 2, police began doubting the validity of Smith's story and launched a simultaneous criminal investigation. Theriot's body was eventually found in a remote area near Lake Mead on Sept. 3.
Smith and her 40-year-old boyfriend, Joshua Oxford, were arrested that day after police recovered Theriot's body. Both were booked on child abuse charges, but have since been charged with first-degree murder, according to court records.
Las Vegas Metropolitan police homicide Lt. Ray Spencer said on Sept. 3, "We do have an idea of how the child was killed. I will tell you that it is absolutely disturbing."
Oxford was in charge of Theriot's younger brother, Brandon, while police searched for Daniel. Prosecutors said Oxford has a previous conviction for child abuse and neglect from 2013 and a battery domestic violence charge. During a court appearance on Sept. 4, prosecutors said Smith revealed the injuries and abuse her children suffered while in Oxford's care.
Child Protective Services took Brandon Theriot to Sunrise Hospital where medical staff reported signs of ongoing abuse. He was also taken into CPS custody.
"This is not an ordinary child abuse, neglect or endangerment type case," Judge William Jansen said on Sept. 5. "This is much more serious."
In interviews with police, Smith and Oxford said they had been dating for a year or two, off and on. They had lived in Las Vegas for two to four weeks in a studio apartment with Smith's two young children. They both said Daniel "had a bad attitude and had been disrespectful" to them, according to police records.
Smith said Oxford "lost it" and spanked Daniel over and over again. After he didn't listen, he poured water on him. When that didn't work, he heated water on a stove and poured that on the boy, Smith said to police. He said 'ow' and Smith watched and did nothing.
Oxford's mother, Kathy Evans, said she was a witness to some of the abuse.
"(Daniel) was in trouble for something before (I got there). I don’t know what it was," she said. "He was standing in the corner when I got there."
The Clark County Coroner's Office said Daniel Theriot had several scrapes and bruises, blunt force injuries, broken ribs and a brain bleed.
"The autopsy of that child indicated ongoing abuse," prosecutors said. "There is evidence that was at the hands of both individuals charged in this case."
When Smith and Oxford later returned to their apartment, Evans said Daniel was asleep and the couple left him alone. According to the arrest report, Smith later found Daniel dead on the floor. She and Oxford put his body in a plastic tub, then drove to a secluded area near Sunrise Mountain where Oxford dumped the boy's body.
Smith told police she and Oxford made up the story about the boy's disappearance to avoid prison.
Smith and Oxford are scheduled to appear in court on Aug. 1 at 8 a.m.