Before the 1993 siege at Waco, Texas, ended in a horrific fire, a group of Branch Davidian children provided startling insight into the structure and motivations of the apocalyptic religious sect led by David Koresh.

The standoff began on Feb. 28, 1993, when 76 agents from the Bureau of Alcohol, Tobacco and Firearms arrived at the Mount Carmel Center compound with a search warrant to look for illegal weapons. A shootout between federal agents and Branch Davidians ensued, killing four ATF agents and six Davidians.

Watch "Truth and Lies: Waco," the documentary event, on Thursday, Jan. 4 at 9 p.m. ET on ABC

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In the early days of the standoff, almost two dozen children were released into the care of the Methodist Children’s Home in Waco, where they were cared for by a team of trauma specialists.

“They had a pervasive belief that David Koresh was God,” chief psychiatrist Dr. Bruce Perry, who worked with 19 of the Davidian children, told ABC News.

“David was not to be questioned,” Perry said, adding that two adolescent girls in the group had already been selected by Koresh to join his harem of wives. “A set of young girls had been designated to become his brides. And they were disappointed this wasn't going to happen.”

Waco Tribune Herald/AP

According to former Davidians, Koresh could pick and choose among the women inside Mt. Carmel -- even the married ones.

“It’s sick and it’s perverted and yeah, it’s one of the things about David Koresh that probably bothers me the most,” former Davidian David Bunds, who was in his mid-20s at the time, told ABC News. “My position now is that David Koresh was a pedophile. I wish I would have done something. I don’t know what I would have done but I wish I had done something.”

Kiri Jewell, who told ABC News in a 2003 interview that her mother Sherri was one of Koresh’s wives, said she herself became Koresh's youngest "bride" when she was just 10 years old, and later testified before Congress that Koresh molested her at a motel. By Jewell’s account, Koresh had as many as 20 wives by the time he died on April 19, 1993.

While Perry doesn't believe any of the children under his care were physically sexually abused by Koresh, but he did say they received other forms of sexual abuse. “They all were exposed to inappropriate sexualized content, language and behaviors,” he said.

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Perry described first walking into a room to meet the children. “One of the littlest kids looked up at me and said, ‘Oh, are you here to kill us?’” Perry said the children were frightened, with resting heart rates twice as high as expected for a normal child.

Former Davidian Joann Vaega, who was 6 years old at the time, was one of the children released early in the standoff. Once on the outside, she told ABC News, “Everything was different.”

“Trying to understand what it’s like to take a bath just seemed very scary to me, flushing toilets scared the bejeebers out of me,” Vaega said. “I had no idea what the heck a basketball was.”

Margarida Vaega, Joann Vaega’s mother, would later perish in the fire on April 19. Joann Vaega has only one possession to remember her mother by. “She gave me her necklace,” said Vaega. “It really is the only thing she had.”

“While we watched them, we learned a lot about the belief system of the Davidians,” Perry said. “One of the things that all of these kids had learned to do, even the really young kids, was march and handle a gun.”

Perry said he also observed startling behavior foreshadowing the events of April 19. He said the children sang apocalyptic songs and drew "end of days"-type imagery.

“Younger kids would draw a picture of the compound with fire coming out of it and I’d say, ‘What’s that?’ and they’d say, ‘That’s none of your business. You’ll find out,'” Perry said.

Rick Bowmer/AP

Dr. Bruce Perry

“It was clear that there was this permeating apocalyptic perspective,” said Perry, adding that he passed along this information to the FBI and told the agency “that they really needed to be very cautious.”

On day 51 of the siege, the FBI launched an operation to remove the Davidians from their compound using tanks equipped with non-lethal tear gas. Officials said the Davidians responded by setting their home ablaze. Only nine survived the deadly fire, all others were killed -- approximately 80 in total, including around 32 women and 21 children. It was the deadliest standoff in U.S. law enforcement history.

“I have to say, I was horrified by what happened,” Perry said. “But I wasn't surprised.”

Watch "Truth and Lies: Waco," the documentary event, on Thursday, Jan. 4 at 9 p.m. ET on ABC

David Koresh, leader of an apocalyptic religious sect, perished with about 80 followers when the compound they shared burned to the ground.

A Congressional investigation concluded that Koresh and his followers set the fire themselves as FBI tanks sought to end a 51-day standoff with the group using tear gas at the group's Mount Carmel Center near Waco, Texas compound on April 19, 1993. The tragedy came to be known as the Waco massacre.

Watch "Truth and Lies: Waco," the documentary event, on Thursday, Jan. 4 at 9 p.m. ET on ABC

Long before he became the prophet and leader of the Branch Davidians, Koresh was just a boy growing up in Texas. Born Vernon Howell to a teenage mother in 1959, Koresh claimed he had memorized both the New and Old Testaments of the Bible by the time he was 18 years old.

“He claimed that when he was a child, God had spoken to him and said, ‘You’re the chosen one. You are my messiah,’” journalist Mary Garafolo, who covered the events at Waco for the news program “A Current Affair,” told ABC News.

Former Davidian David Bunds said when he first met Koresh in the summer of 1981, he thought Koresh seemed “lost.”

“He was kind of a drifter,” Bunds told ABC News. “He had a car that he was driving and he said the Lord gave it to him.”

“He was a very disheveled kind of guy,” he continued. “He was poor obviously. He didn’t have a job, or at least a regular job.”

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By 1983, Koresh had joined a religious sect that called themselves the “Brand Davidians” (Branch Davidian) -- a splinter group of the Seventh Day Adventist Church -- founded by former Seventh Day Adventist Victor Houteff in 1934. Koresh fell under the tutelage of Lois Roden who took over leadership, along with her husband Benjamin Roden, from Houteff after his death in 1955.

“One of the things about being a Branch-Davidian … was you’re supposed to separate yourself from the world,” Bunds said. “The world is the sins, the flesh, the desires of the world, and you’re supposed to be spiritual.”

Former followers said the compound had no running water, heat or electricity and there was Bible study three times a day. Branch Davidian Clive Doyle said Koresh had been interested in music and Lois Roden encouraged him to continue sing and play guitar, which became part of the group’s daily Bible study sessions.

“He believed he was King David,” Doyle told ABC News. “He was using music to reach a lot of people. We're thinking maybe it's a stage name. But it was more than that.”

By 1990, Vernon Howell changed his name to David Koresh. Two years later, he had taken over the group, encouraging the use of guns and preaching an ever increasing brand of apocalyptic prophecy. He believed that the group would someday be under attack by the U.S. government and began stockpiling guns and ammunition.

Former followers said Koresh truly believed he was on a mission from God and was the only one who could interpret the bible and its true meanings for the masses.

“His message changed over the years because he was always looking for the next big thing to teach that would shock people into listening to him,” Bunds said. “It was important for David Koresh… to isolate the group from the world because the world is an influence that is constantly pulling and distracting you from the message.”

Former followers said women had to wear long blouses, and no make-up or jewelry could be worn. They said Koresh would tell them where to sleep and what food they could eat – sugar, processed flour and dairy products were forbidden.

“He taught that we should not eat any dairy products,” Bunds said. “His reasoning was, well, dairy products are made from milk which is baby food. Milk is what you drink when you’re a baby and we’re adults now.”

Sheila Martin, who moved to the compound with her husband and their five children in 1988, said, “It was fun as long as we were being obedient.”

“If we weren’t being obedient in the sense of like, [I] went to the store and bought something that, you know, it was being selfish,” she continued. “He always would let us know it wasn’t right and we should’ve done [it] differently, and many times it was in front of everyone.”

Former followers said discipline was constantly administered. Joann Vaega, who was 6 years old when she left the compound, said she remembers being hit regularly and “as a kid, being disciplined was like a 24/7 thing.”

“There’s nothing that you could do right, is how I felt as a kid, that fear, that nothing you can do is going to be good enough,” she said. “You’re raised with just fear. Everywhere is fear.”

Vaega said Koresh constantly told them the end of the world was coming, they were “the chosen people to survive because David was the son of God.” She said they were taught to prepare “for war,” and that the “end times,” as predicted in the Book of Revelation, were near.

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Koresh had his own children too. Dana Okimoto, who gave birth to his son Sky Okimoto, told ABC News in a 2003 interview that children were kept in line by a wooden paddle and faced severe beatings for minor infractions like spilling a glass of milk. She said she remembered being so under Koresh's control that she beat Sky until he bled.

"If there was one thing I could take back, I would take back the spankings," Dana Okimoto said at the time. "I felt like the most evil person in the world to be beating my baby this way. But this was what God wanted and needed from me."

Former followers said Koresh would separate families from each other. Bruce Perry told ABC News that if Koresh thought a mother and a child had a tighter bond than between him and the child, then Koresh would tell the parent, “You haven’t been disciplining them adequately so I’m going to have this mother raise your kids.”

“Everyone as a community was taking care of kids,” Vaega said. “It wasn’t your parent was your parent. Everyone was supposed to be a parent … anyone could spank anyone because everyone was the parent.”

Doyle said Koresh asked his followers, including married couples, to embrace celibacy.

Then, Bunds said, Koresh claimed all marriages in the group were dissolved and that all of the women would be his “wives” if he wanted them, even though Koresh was legally married to one woman, Rachel Jones.

“David Koresh’s justification for taking all of the women for himself was theological … he’s the one that had the power, he’s the one that had the authority to ‘give the seed,’” Bunds said, adding that if he had sex with a woman, Koresh would say she was in the ‘House of David.”

“So yeah, being a member of the House of David was a privilege,” he said.

“Basically David would be having the children with some of the wives,” added former follower David Thibodeau.

There were allegations from some of Koresh’s former followers that it wasn’t just the adult women he wanted, but he also pursued several of their daughters, some of whom were teens or even younger. Kiri Jewell, who told ABC News in a 2003 interview that her mother Sherri was one of Koresh’s wives, said she herself became Koresh's youngest "bride" when she was just 10 years old, and later testified before Congress that Koresh molested her at a motel. By Jewell’s account, Koresh had as many as 20 wives by the time he died on April 19, 1993.

“It’s sick and it’s perverted and yeah, it’s one of the things about David Koresh that probably bothers me the most,” Bunds said. “My position now is that David Koresh was a pedophile… [and] I wish I would have done something. I don’t know what I would have done but I wish I had done something.”

Looking back on his time inside Koresh’s sect was emotional for Bunds, who said it was difficult at the time to fully understand what was going on around them.

“I’ll call it a cult, that’s what it was ... it’s people doing things they wouldn’t normally do, like giving up their wives and letting their children have sex with adults, which is crazy, but that’s what you do when you’re in a cult,” he said. “Someone says they have authority and then impose upon your rules and restrictions and expectations and it gets down into your soul, it really screws you.”

Watch "Truth and Lies: Waco," the documentary event, on Thursday, Jan. 4 at 9 p.m. ET on ABC