"Detectives determined the falling sandbag was not an accident, but a deliberate act and probable cause to charge the juveniles was established," the department said.
Byrd was taken to hospital in critical condition. He died three days later from blunt-force trauma to his head and neck, authorities said. The teens were arrested shortly after Byrd was injured and the charges were upgraded to murder.
Byrd's cousin, Shaveontae King, told the Toledo Blade that the 22-year-old was engaged to be married and had a 1-year-old son. He had been on his way to meet friends in Toledo. He was "young, energetic, outgoing, lovable," King said.
"My auntie has to bury her son. He's gone. He's never coming back," King said. "She's holding up the best she can."
Olender said it was unlikely any of the four teenagers would be tried as adults; Ohio state laws don't allow for 13-year-olds to be tried this way and the children lacked significant criminal records, she said.
Olender said the children were charged with two counts of vehicular vandalism because they had struck another car with a rock, though no one was injured.
In October, prosecutors in Genesee County, Michigan, said five teenagers would be tried as adults after a passenger was killed by a rock, also on Interstate 75. The five teenagers face a potential of life in prison.
According to the Toledo Blade, the bridge over the highway from where authorities said the sandbag came was under construction and was missing some of its protective fencing. Contractors remove tools from the site at night, but leave the sandbags, an Ohio Department of Transportation spokeswoman told the newspaper.