Police say a Florida father has confessed to trying to kill himself and his 10-year-old son whom authorities found -- along with his dead twin sister -- inside a pickup truck along a busy interstate, convulsing and covered with toxic chemicals.

Jorge Barahona, 53, faces aggravated child abuse charges after a state worker found him and his son Monday on the side of Interstate 95 in West Palm Beach. The boy, Victor, was convulsing from seizures, dripping in an unknown chemical so toxic it sickened rescue workers, as his father lay on the ground doused in gasoline. The boy was airlifted to a hospital where he remains in critical condition.

The body of the boy's twin sister, Nubia, was found hours later wrapped in plastic bags and wedged between chemical containers inside the pickup truck.

Police have charged Barahona with aggravated child abuse and more charges are expected. He is expected to make his first court appearance Thursday.

Barahona told officers he put his dead daughter in the truck and began driving with his son, intending to commit suicide. He was distraught, gave his son a handful of sleeping pills and, with the boy's head in his lap, poured gasoline on himself, according to police documents.

He told police he intended to light himself on fire but said he could not do it because the boy was in the truck, according to the documents. When police asked why he didn't have similar burns as his son, he said some of the gasoline must have splattered on his son.

It remains unclear how Nubia died.

"He was stating he placed his daughter in a plastic bag," Chase Scott of the West Palm Beach Police told wsvn.com. "Being distraught over her death, he drove here from South Florida accompanied by his son Victor."

An angry judge, meanwhile, grilled state child welfare officials Wednesday over missed opportunities to help the twins after an anonymous abuse allegation was called into a hotline Feb. 10 -- four days before the children were found by the highway assistance worker.

The caller said the twins' feet and hands were bound with duct tape and they were kept in a bathtub as punishment. Child welfare officials also believe the girl was being starved.

The state officials described a disturbing picture of a Jorge and Carmen Barahona, who adopted the twins, an 11-year-old autistic boy and a 7-year-old girl from foster care. The couple has been the focus of at least three abuse allegations in the past several years, but nothing ever came of them.

The Barahonas' other adopted children have been placed in a foster home.

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The Associated Press contributed to this report.