David "D.J." Creato Jr. was secretly recorded speaking about the spirit about a month after the slaying, the boy's mother, Samatha Denoto, said on the first day of testimony in the case against him.
Denoto said she recorded Creato at the request of criminal investigators.
"We talked about what else could have happened to him. He had told me that maybe the spirits told him to walk down to the woods which is completely odd and unexplainable," she said.
Earlier, assistant prosecutor Christine Shah told jurors during opening statements that the 23-year-old Creato was consumed with jealousy at the time his son's body was found in woods by the Cooper River near their Haddon Township home in October 2015.
The prosecution says Creato killed Brendan Creato to stop his 17-year-old girlfriend, who was away at college, from leaving him. It says Brendan suffered "homicidal violence."
Jurors heard David Creato's 911 call, in which he told police he had just woken up and his son was missing.
"He wandered out of the house," Creato says on the call. "He must have unlocked it and left."
Shah said that when investigators walked the area at night, they found the area to be exceptionally dark, and that family members said that little Brendan was afraid of the dark.
"It was incredibly dark, the kind of dark where you can't see own hand in front of your face," said Shah.
"The night this happens, Creato's cellphone never leaves the sector where his apartment is," said Creato's attorney, Richard Fuschino Jr. "It never moves toward the area where the body was found. Why is this significant? Because when police did a thorough search - twice - of his apartment, they don't find any flashlight."
After a three hour search, Brendan was found in Cooper River Park, partially submerged in a creek. The scene was about a half mile from his father's home.
Creato is charged with murder and child endangerment. His lawyer told jurors there's a "complete lack of evidence" in the case.
Fuschino said Creato loved his son. He said, while Creato's spiritual nature may make people uncomfortable, that doesn't make him guilty. He said Creato, who has pleaded not guilty, was honest and upfront with police.
Testimony is to resume Tuesday.
The jury is expected to visit the park where the boy's body was found in a stream.
A memorial for Brendan was removed from Cooper River Park over the weekend. Creato's attorney expressed concern over the possible impact of the memorial on the jury.
The Associated Press contributed to this report.
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