A man with Down syndrome who police said was nonverbal and had the cognitive ability of a 1-year-old died in a hot van while his caregiver slept in the driver's seat after taking drugs, authorities in Florida said.

Joshua D. Russell was arrested Friday and charged with one count of aggravated manslaughter in connection with the death of 35-year-old John LaPointe.

LaPointe, a resident of Crossroads of Pinellas group home, was found in the backseat of a van on May 9 after he was left in the vehicle without air conditioning for several hours as Russell napped in the front.

"Let's just call it what it is, this poor guy baked in that car," Pinellas County Sheriff Bob Gualtieri said at a news conference Friday. "I'm sure he had to suffer. ... It had to be absolutely horrific in that car for that man."

Authorities determined the temperature inside the vehicle that day had climbed to about 125 degrees. Gualtieri said he is not sure why the heat did not affect Russell the same way it did LaPointe.

Authorities were alerted to the death just after 5:30 p.m. on May 9 when the agency received a call about a man unresponsive in a vehicle in Seminole, about 25 miles from Tampa. When deputies arrived, Russell had fled and LaPointe had been pronounced dead.

John Matthew Lapointe. Sorenson Funeral Home

Russell, an employee of the group home, was found nearby with a gun threatening to kill himself, according to Gualtieri. He was eventually arrested and booked into the county jail on a charge of carrying a concealed weapon.

Russell told authorities that he took LaPointe to a doctor's appointment earlier that day and then stopped by his own house to use a substance called kratom, Gualtieri said. LaPointe had been left inside the van while Russell was in the home.

Kratom is a substance made from a tree that is sometimes used as a recreational drug, the sheriff's office said in a news release. The U.S. Food and Drug Administration has warned people not to use the supplement, which grows naturally in Southeast Asian countries because it "appears to have properties that expose users to the risks of addiction, abuse, and dependence."

When Russell returned to the vehicle, he told authorities that he attempted to drive back to Crossroads but started to feel sick so he turned around, parked the van in his driveway and fell asleep. He said the van had poor air conditioning and he did not leave the car on because it would overheat.

Russell said he believes he had been asleep for two or three hours when he woke up "extremely hot and covered in sweat," Gualtieri said. LaPointe, who had been in the back with a seatbelt on, was slumped over and not breathing, Russell told investigators.

Joshua D. Russell. Pinellas County Sheriff's Office

Gualtieri said Russell told detectives that he attempted CPR and when that did not work he went into the house and grabbed a gun with the intention of killing himself. He then called his mother, got back into the van and started to drive to a location where he thought his mother was.

Russell's mother called 911 after meeting her son, according to Gualtieri. An autopsy was conducted on LaPointe and a medical examiner determined that his cause of death was due to overheating.

Russell was booked into the Pinellas County jail on a $50,000 bond. The Crossroads of Pinellas group home did not immediately return a request for comment.

In an online obituary, LaPointe's family called his death a tragedy.

"John has an infectious smile, angelic sweet gentle spirit and so enjoyed watching Barney cartoons on his tablet," it read. "John was a beautiful human being loved by all and will forever be in our hearts."