Updated

Yet another fight in an "ugly" and violent relationship between two 21-year-olds left their 9-month old shot to death in his highchair, his great-grandmother killed with a shotgun as she tried to run for help and their families in mourning, authorities and relatives say.

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 morning in the rural home outside Manning in central South Carolina.

"It was an ugly relationship," said Terrence Whitfield of Kingstree, who identified himself as Kaisha Carraway's step-father. "He was like a Dr. Jekyll-Mr. Hyde kind of person. They'd had trouble for some time."

Sometime during a dispute between the couple Wednesday, Johnson, a National Guardsman, killed his son with a 12-gauge shotgun then felled the elder Carraway as she had tried to flee her home and was calling 911 for help, the sheriff said.

He also shot and wounded Kaisha by taking aim at her through a bathroom door inside the rural home.

"He tried to kill her but he ran out of ammunition," Garrett said in a telephone interview. "He went there with every intention of doing what he did."

Whitfield said Kaisha was living with her grandmother, Maxine, who was trying to help her out.

"She was just a wonderful person, a generous person," he said of the great-grandmother. "She didn't deserve this."

After the shooting, Johnson tried to fool Garrett's deputies by forcing Carraway and their 2-year-old into his car and flagging down an officer on the road who was responding to the 911 call.

But the deputy spotted blood spatters on Johnson's shirt and asked to be led to the scene, which Johnson tried to blame on someone else.

"We had five, six cars and deputies there to meet them," Garrett said. Officers separated the two adults and Carraway told them what had happened and Johnson was arrested, the sheriff said.

Garrett said Johnson had been free on bail on a charge of aggravated criminal domestic violence from December of last year against Carraway.

"I don't know how he got out of jail," Whitfield said in a telephone interview.

"It's all so useless," he said about the loss of his family members.

Johnson is an Apache helicopter mechanic with the South Carolina Army National Guard, said spokesman Col. Pete Brooks. Johnson, who has never deployed on full-time active duty with his unit, joined the Guard in July of 2007 and is a private first class, Brooks said.

A decision on his future in the military depends upon the outcome of the civilian court process, Brooks said.

No bond hearing has been scheduled on the new charges and Johnson has not sought an attorney, Garrett said. A search of phone records did not produce a number for Johnson and calls placed to several Johnson families in the area did not locate any family members.

Johnson confessed to the killings late Wednesday, Garrett said.