Authorities are trying to determine if driver impairment led to a car crash in Gilbert that left the son of a Pinal County sheriff dead at the scene along with an infant.

Gilbert police identified the victims as 22-year-old Cooper Lamb and his 1-year-old daughter.

Pinal County authorities said Cooper Lamb was the son of Sheriff Mark Lamb and the child was his granddaughter.

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Cooper Lamb’s fiancée, who was the child’s mother, remained hospitalized in critical condition.

Police said the three were in a car that was struck by a truck around 4:30 p.m. Friday in Gilbert.

Arizona’s Pinal County Sheriff Mark Lamb’s son and granddaughter were both killed in a fatal car crash possibly caused by someone driving under the influence. 

The driver of the truck was injured and was arrested on suspicion of DUI, according to police.

That person’s name has yet to be released.

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"Our hearts are broken," Mark Lamb said in a Facebook posting. "We are praying for our precious Caroline who is still in critical condition. We would also like to express our gratitude for those citizens and first responders who rendered air to our son Cooper and our granddaughter."

"This is heartbreaking. Something no parent should go through," Arizona Gov. Doug Ducey said in a statement. "My prayers go to Sheriff Lamb, his wife Janel and their family."