COLUMBIA -- Yet another fight in a violent relationship between two 21-year-olds left their 9-month old shot to death in his highchair, his great-grandmother shot to death as she tried to run for help and their families in mourning, authorities and relatives said Thursday.

Justin Jeremiah Johnson was in the Clarendon County Detention Center in Manning after confessing to killing his son Jayden Carraway and 59-year-old Maxine Briggs Carraway, authorities said.

He is charged with two counts of murder, kidnapping and attempting to kill the child's mother, Kaisha Tiera Carraway, said Clarendon County Sheriff Randy Garrett.

The couple also have a 2-year-old daughter, who witnessed some what happened Wednesday in the rural home outside Manning.