Salt Lake County sheriff's detectives are calling the death of a 2-year-old boy a homicide.

Sunday night, deputies were called to assist paramedics on a call of a toddler who went into cardiac arrest at his home near 5500 West and 5100 South, said sheriff's Lt. Paul Jaroscak. Alejandro Gabriel Lucero was flown to Primary Children's Medical Center where he died about 90 minutes later, he said.

During the autopsy the next day, however, the state Medical Examiner's Office discovered the boy's spinal cord was severed, prompting the sheriff's office to launch a homicide investigation.

"It's our believe the injury was caused by another person," Jaroscak said.

Homicide detectives learned the boy's 17-year-old mother and her 26-year-old boyfriend were taking care of Lucero the night he died.

"The original statement made by the mother was she was holding the child when it began to have seizures," Jaroscak said.

Following extensive interviews with the pair, investigators learned the boyfriend, Sergio Martinez-Gonzalez, is not a legal citizen of the United States and he was later booked into the Salt Lake County Jail on an immigration detainer.

Martinez-Gonzalez is not the father of Lucero, but he and Lucero's mother have 5-month-old twins together who were taken into state protective custody following his arrest.

The investigation for detectives is difficult in this case because there is very little evidence where authorities believe the injuries may have happened — the child's house. Paramedics did not notice any other visible injuries and detectives were unsure if Lucero had any prior fractures or injuries that were already in the process of healing.

"There is no murder weapon, no blood spatter evidence," Jaroscak said. "It's a circumstantial case. We'll look at the statements given, match them with the medical examiner's report, look into the history of any other illnesses of the boy and the other children in the home."

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