A mother and her boyfriend were on suspicion of child abuse after a 3-year-old boy was found dead in a remote area near Lake Mead National Recreation Area, Nevada. In this representational image, police vehicles line Las Vegas Boulevard following the mass shooting Oct. 4, 2017. REUTERS/Chris Wattie

A mother and her boyfriend were arrested Monday on suspicion of child abuse after a 3-year-old boy was found dead in a remote area near Lake Mead National Recreation Area, Nevada.

Las Vegas Metropolitan Police Homicide Lt. Ray Spencer said the boy's mother, 20-year-old Cassie Smith, and her boyfriend, 40-year-old Joshua Oxford, were not charged in the death of Daniel Theriot but arrested on suspicion of child abuse in connection with the treatment of the 3-year-old's younger brother. They were likely to be charged with murder in the death of the toddler, the police said.

The child's body was found Monday morning, a day after his mother reported him missing. The mother called cops at around 9 a.m. local time (12 p.m. EDT) Sunday and reported she was at Sunset Park with the toddler and he wandered away while she took a phone call. A search was launched immediately.

The police, however, began to have doubts about Smith's story after no one at the park recalled seeing her and the child together.

"If your child is missing, and your 3-year-old comes up missing near a lake, and you're trying to locate your child — there's going to be people at that park who are going to see you trying to locate the child. And we could not find anybody,” Spencer said, NBC News reported.

After searching the immediate area, the officials went to check the apartment where Theriot lived and came in contact with Oxford and the toddler’s younger brother. Child Protective Services transported the 2-year-old to Sunrise Hospital where the medical staff discovered signs of physical abuse.

Investigators conducted further interviews and eventually found Theriot’s body Monday morning. It was, however, unclear what led them to the area.

Smith and Oxford were taken to Clark County Detention Center and booked on one count of child abuse or neglect. Police said Theriot was a victim of child abuse too.

“It’s absolutely disturbing on how the child, we believe, was killed,” Spencer said, without elaborating on the details.

"There is nothing accidental about this investigation, as far as the death of this child," he said, adding the post-mortem would provide more details on the cause of death. "We believe the murder actually occurred within the previous 12 hours from the original 911 call.”

The officer said it does not seem like the local child protective services had any past contact with the family; however, officials are looking at other jurisdictions.

Red Rock Search & Rescue, a helicopter, several law enforcement agencies and an FBI joint child abduction rapid response team were involved in search for the missing child.

The toddler’s death comes a little less than two weeks after Las Vegas police found a 3-year-old girl dead in a duffel bag inside her family's apartment. Spencer referenced the case in Monday's press conference and said, “it's deeply disturbing that I'm here talking to you, very similar details, a week and a half after the last child that was a victim of being murdered inside a house with the people who are supposed to care for them."

"Having children is stressful. Having toddlers are stressful. Having a baby is stressful. If you find yourself in a situation where you cannot care for your child, you can take your child to a fire station, and you can take your child to a hospital. But this is absolutely — I mean, it's hard to deal with," he said.