When Timothy Jones Sr. learned his grandchildren were missing, a deep, unshakable dread set in, and he feared his own son had killed them.

“I remember I told my wife, ‘I know he’s killed them,’” the patriarch tearfully recalled to Fox News Digital. “I just don’t know where they are. But I know he has. I just know it in my heart. I could feel it.”

Timothy Jones Jr. admitted to killing his five children, ages 1 to 8, in their Lexington County, South Carolina, home in August 2014.

He drove with their bodies in his SUV for nine days before dumping them in five garbage bags on a hillside near Camden, Alabama.

Jones Jr. was later arrested at a traffic checkpoint in Smith County, Mississippi, after an officer smelled an odor of decomposition, The Associated Press reported.

His case is now being examined in an episode of Investigation Discovery’s (ID) true-crime series, “Evil Lives Here: My Child the Killer.”

It focuses on parents forced to confront the unthinkable, that the children they raised and loved have become capable of monstrous acts.

Before the murders came to light, Jones Sr. said he hadn’t heard from his son.

Then came a call from his grandchildren’s school, concerned about their absence.

When he reached out to one of his son’s friends, he learned that Jones Jr. hadn’t been seen in the previous day or two at work.

“Then the police officer called me from Mississippi,” said Jones Sr. “I tell him, ‘I just want to make sure he is OK and the children are with him.’ He said, ‘What children? There are no children with him. We found a little bit of blood in the car, and we’re having it checked. It could be animal blood.’”

Panicking, Jones Sr. begged to see his son. At the trial, authorities testified that they allowed the meeting, hoping a face-to-face confrontation might break Jones Jr. and reveal what had happened to the missing children.

When Jones Sr. entered the interrogation room, he was stunned by what he saw. He said it was like staring at a wild animal.

“He’s just a blubbering mess,” said Jones Sr. “I’d never seen this person before. I didn’t know that boy. But I just wanted to know where my babies were. And he was all over the place.”

That’s when Jones Sr. said his son suddenly jumped up and snarled, “I could kill you right now.”

“I told him, ‘You can’t kill me. I love you,’” said Jones Sr. “He was going to put his hands around my throat. He never did. He just sat back down and started crying. But I just didn’t have a good feeling. I’m trying to get him to tell me anything.

“One cop got p—-d off a little bit, jumped up and said, ‘There’s a substantial amount of blood in that damn car. I want to know what the hell is going on.’ I just looked at him in shock, like, ‘What? You just told me there was a little bit of blood, and you were going to test it.’”

Jones Sr. offered to go with his son to find the children.

“I begged him, ‘Son, please, those children are out there by themselves with animals,’” said Jones Sr. “He told me, ‘You can’t go with them.’ I said, ‘That’s fine. Just take them to those kids.’”

Jones Jr. eventually led authorities to the bodies of his five children.

“And, of course, my life’s changed ever since,” said Jones Sr.

“I knew he killed them. But how could he? What man could possibly do this to their own children?”

Jones Sr. remembered his son as “a good little boy” who grew up without his mother.

Raising him on his own, Jones Sr. worked multiple jobs but still made sure to be there, fixing him breakfast, taking him to school and spending long afternoons by his side.

But, looking back, there were signs that something wasn’t right.

“He was just a normal boy,” said Jones Sr. “I didn’t have any trouble with him until he was about 9. Then he shot the neighbor in the back of the leg with a BB gun, which I got him for Christmas. He had this little puppy that he slapped and swore at. It seemed unusual. But I talked to him about it, and we never had that issue again.”

In high school, Jones Jr. became increasingly angry, worrying his father.

“We got in a few tussles and got into arguments,” said Jones Sr. “But I thought it was no more than any other teenage kid.”

In 2001, Jones Jr. was charged with a crime spree that included burglary, car theft and forged checks. He was sentenced to seven years in prison. When Jones Jr. was released, he was seemingly a changed man.

“We used to go to church,” said Jones Sr. “But when he came back [from prison], he’s all hell-bent on living by the Bible. I told him, ‘Son, I understand what you’re trying to do, but you’ve got to remember, the Bible is the guideline of life. You can’t follow every rule in there because you can contradict yourself, and it’s just too tricky.’ But he was convinced that that’s the way it was going to be.

“I went to church with him a few times,” he said. “He would get up and act crazy. I didn’t expect it. I almost felt like he was in a cult. He was talking in tongues.”

Jones Jr. married Amber Kyzer in 2004. The union was highly tumultuous, especially in the years leading up to the killings. The relationship deteriorated into a contentious custody battle, with Jones Jr. having primary custody. They divorced in 2012.

“In the beginning, he was a great father,” said Jones Sr. “Seemed like a good husband. We would do everything we could to help with the kids. But when they divorced, I just thought, ‘My God, it’s going to be really hard for one man with five children who has to work.’ We really wanted to help. We tried.

“I pleaded with him, ‘Let us help you. You have family who could help. I’m here.’ But all he said was, ‘It’ll be all right.”

On their last Christmas night together, the two men got into a heated argument.

“He told me how I never loved him, never cared for him,” said Jones Sr. “Now, at that point, this had been going on many, many times. He would tell me how I didn’t love him. I finally said, ‘I gave up my life for you, raised you by myself. 

“I did everything I possibly could. I tried to give you the best life I could. How am I a bad dad? What did I do? Tell me what I did now, and maybe I can fix it.’ And he just said, ‘I never want to see you again. You can go f— off.’”

Jones Sr. said he would reach out to his son, hoping he could see him and the kids.

“I remember he said, ‘Would you like to talk to the children?’ Now I was supposed to see him the next day. So I said, ‘You know what, Timmy? Let’s surprise them. They’ll be really happy because they loved coming over to ‘papa’s big house,’ as they called it. I built a pool and everything for them. But the next day, he went missing.”

“That’s always been my biggest regret, not speaking to the babies one last time,” he tearfully said.

During the trial, Jones Jr.’s defense team argued that he suffered from mental health issues.

Defense lawyer Boyd Young claimed the prosecution ignored evidence that proved Jones Jr. was insane. However, prosecutors maintained that Jones Jr. knew what he was doing.

The jury convicted him of five counts of murder and sentenced him to death.

Jones Sr. said he hasn’t spoken to his son.

“I just can’t,” he said. “I’m falling apart. I’ve lost my business. I damn nearly lost my home. I knew he was sick. But after the trial, he called and just acted like it never happened. I’m here falling apart, and he’s just laughing, giggling. I couldn’t do this anymore.”

Jones Sr. admitted he will always carry guilt with him for the rest of his life. He still wonders what he could have done to help his son and grandchildren.

“There’s no way I cannot blame myself,” he said. “Those babies should be here. I should have done something before it went too far. I knew he was going to have a hard time with five children. I knew all these things. I should have done more. I’ll regret that until the day I die.”