Story highlights The bodies of Atira Hill, Laterry Smith and Jaidon Hill, 7, were found overnight

The family was last seen Friday in a car

That vehicle was later found flipped and on fire

Authorities have arrested Timothy Burns, 42, on suspicion of arson, a sheriff says

Heartbroken and baffled.

That's how friends and relatives of a Mississippi family described themselves the day authorities said they'd found the bodies of Atira Hill, Laterry Smith and Jaidon Hill, 7.

The mother, stepfather and boy vanished last week

"We went to bed last night still praying they would be brought home safely, but unfortunately, that did not happen," said Vinson Jenkins, Hill's cousin. "To my knowledge, we don't know why anybody would want to do any harm to them."

Authorities don't know why yet either.

When the family first disappeared, they hoped they had a simple missing persons case on their hands.

The family was last seen Friday in a car. An investigation kicked into gear when that vehicle was later found flipped and on fire.

Bloody clothes belonging to the victims were discovered next in a gas station Dumpster. And then the bodies were located.

They were found overnight in a wooded area, Copiah County Sheriff Harold Jones said Tuesday. They had been shot to death.

"I don't know how anyone could be so callous and cruel to do this -- take a life, especially the life of a child who hurt no one and didn't deserve what he got," said Angela Ashford, another family member.

Authorities have arrested 42-year-old Timothy Burns on suspicion of arson, Jones said. He is also being held for "investigative purposes" in connection to the killings, according to the sheriff.

It was not immediately clear whether Burns had retained representation. He was being held at the jail in Copiah County, southwest of Jackson.

The investigation is ongoing, but at this point, authorities believe Burns was driving the car, got into an accident and then set the vehicle on fire, Jones said.

It's not known whether the victims were in the car at the time of the accident. Nor is it known whether Burns and the victims had ties, though the sheriff believes they did not.

He said Burns led authorities to the bodies.

"We're investigating. This just happened," Jones said.

According to CNN affiliate WAPT, Jaidon was a student at Stonebridge Elementary School in Brandon, Mississippi.

A prayer vigil was held Tuesday night at the school, where a flag was lowered to half staff.

Hill worked as a nurse's assistant at the University of Mississippi Medical Center, while Smith was a Sheetrock installer, WAPT said.

According to Hill's mother, Judith Hughes, Hill called early Saturday to say she and Jaidon were on their way to meet Smith's relatives to "take care of some business."

Hughes said she asked her daughter if everything was OK. She said it was.

The phone signal was weak, and the call dropped. Hughes tried calling back, but the call went straight to voice mail.

Hughes said Jaidon lived with her and that he was meant to spend the weekend with his mother.

After the family's car was found flipped, Hughes said she went to the home where Hill and Smith are believed to have lived. It was empty, she said.

Hughes' house was full Tuesday as family members gathered to mourn and to try to makes sense of what happened.

"Atira had such a big heart, why her?" asked Antionetta Taylor, one of Hill's best friends. "She never bothered anybody. She was so young -- and Jaidon was innocent."