Joshwa Carlisle, 22, was arrested Monday and preliminarily charged with two counts of murder and one count of arson.

The bodies of Tracie Shannon, 25, and her 9-month-old daughter, Juliana, were found in her apartment in the 5500 block of Old Colony Road, near 56th Street and Interstate 465, on Sept. 19.

According to the probable cause affidavit released Tuesday, investigators said they believe Carlisle sprayed the infant with an accelerant, likely lighter fluid, and then lit her on fire in her crib.

Carlisle is also accused of killing Tracie by suffocating her and lighting her bedroom on fire.

Police said they interviewed Carlisle the day of the fire and that there were lingering discrepancies in his story from the beginning.

Joshwa Carlisle

Shortly before the fire, a paternity test had confirmed that Carlisle was Juliana's father, and Tracie had asked for $200 a week in child support, according to the probable cause.

Police said Tracie had also led Carlisle to believe that she was pregnant with his twins, and that he had agreed to leave his wife to move in with her and raise the children.

In an exclusive interview with 6News, Tracie's aunt, Patrice Davis, said Tracie and Carlisle had a rocky relationship. She suspected him of killing Tracie and the baby from the beginning.

"We had an idea of who did it, but we had to let the police do their job and gather enough evidence to put the person away, and they were able to find him today, so I'm really excited about that," Davis said.

Tracie's uncle, Eon Davis, said he can't fathom how a person would kill their own child.

"To burn your child alive that can't defend herself is a very weak way of trying to get rid of his responsibilities," he said. "That's not a man to me. That is a weak coward."

Carlisle was being held Tuesday without bond at the Marion County Jail. He refused 6News' request for an interview. An initial court appearance was set for Wednesday morning.