But in between Powell's dark adolescence and grisly murder-suicide, there was a time of light and love with Susan Powell, those close to the couple said.
"Susan and Josh got married, and he seemed to have come around pretty well," Josh Powell's older sister, Jennifer Graves, told "20/20." He seemed to be in a pretty decent place. And I had really high hopes for their marriage, that it would be a successful, happy, good one."
Josh Powell and Susan Cox, each the children of churchgoing families, met at a church function. They were engaged when Susan was just 19 and married in 2001.
"At the very beginning they were, you know, happy, holding hands, hugging, kissing each other," said Susan Powell's sister, Denise Cox. "You thought [they were] a perfect couple, a very happy couple."
Those who knew Susan Powell said she was warm and open -- qualities that endeared her to her neighbors in West Valley City, Utah, where the couple had settled several years after their marriage. Josh Powell was not as popular.
"We all love Susan and we tolerate Josh because he comes along. It's part of the package -- that's how most people felt," former Powell neighbor John Hallewell told "Nightline" recently. "She was always worrying about other people, where Josh was always the opposite. He was only ever concerned about himself, which made things, sometimes, a little difficult."
Susan Powell's parents, Chuck and Judy Cox, found it strange when Josh Powell refused to drive his wife to the hospital when she went into labor with their first child, insisting that her parents take her instead because he had to finish something.
He finally did show up at the hospital two hours later.
"And what he had to do was, he wanted to back up his hard drive before he left," Chuck Cox said.
Graves said she watched as her younger brother, Josh Powell, "faded out."
"As the, the years progressed, I saw him go downhill, you know, slowly at first," she said. "He kind of just regressed a little bit. And then the last few years before Susan's disappearance, it just seemed to accelerate and he seemed to get worse and worse."
Friends said Josh Powell became so controlling of his wife, it became legendary among those who knew them. She had to get his permission just to use the family car and had to follow a strict procedure in order to spend any money.
"He would give Susan an amount of money -- and on grocery shopping, he also had a spreadsheet that she was to look at through ads and find the cheapest price of things," said a friend, Michelle Oreno. "When she went shopping, she came home and she had to enter every single item into that spreadsheet. And if she spent more than a couple of cents more on a can of beans, Josh would really yell at her and get angry."
Josh Powell wouldn't even let his wife spend money on socks, insisting she knit them instead, said Denise Cox.
She said her sister considered leaving Josh Powell but didn't do so for fear of what would happen to the couple's two children, Charles and Braden.
"When I told her to leave with the kids, she told me that he had told her, 'Over my dead body will you have those boys. They're mine,'" Denise Cox said. "The boys were a possession to him. They were his possessions."
Josh Powell wasn't the only man creating havoc in Susan Powell's life. She told friends her father-in-law, Steven Powell, made a pass at her and tried to fondle her chest.
Susan Powell's friends told "20/20" that Josh Powell didn't defend his wife against his father.
"They had a very heated argument about Steve where she was talking about him and Josh would kind of excuse him, [saying], 'That's just my dad. You're blowing things out of proportion,'" Oreno said.
Josh Powell himself may have suffered at his father's hands.
Documents obtained by "20/20" from Steven Powell's 1992 divorce from his wife, Terrica Powell, paint a disturbing picture of Josh Powell as a severely troubled teenager under the thumb of an abusive father.
Terrica Powell wrote that Josh was exposed to pornography by his father at a young age, that he once tried to commit suicide during his early years and, most shockingly, he threatened his mother with a butcher's knife after she asked him to do the dishes.
She said Josh Powell's father had "explosive behavior" -- including severe spankings -- that hurt the son. Yet, the teen also sought his father's attention and approval.
Terrica Powell declined a request for an interview.
Josh Powell claimed his wife had her own faults. In a 2011 interview with "Good Morning America," he accused her of erratic behavior and said she once left the house in her underwear.
He defended himself, too.
"People who know me know that I'm a good dad," he said. "I work hard. I put my sons first. I was a good husband. I took care of my family."
Still, years after his parents' marriage collapsed, Josh Powell was facing the meltdown of his own relationship.
Before Susan went missing in 2009, the couple had begun counseling, said Graves, but it wasn't going well.
"It was clear to the counselor that there was no progress being made," Graves said. "Josh wasn't doing his part. And so the counselor was frustrated, Susan was frustrated. They weren't getting anywhere."
Graves believes that Susan Powell was finally ready to call it quits.
"I think her intent was that they were going to get a divorce," she said. "If this last-ditch effort of counseling didn't work, they were gonna get a divorce."
Susan Powell was reported missing Dec. 7, 2009, in Utah. Josh Powell was the only named person-of-interest in the disappearance, but he was never charged. He continually denied involvement in his wife's disappearance and later moved himself and his sons to live with his father in Washington state.
The couple's two sons were placed in the custody of Susan Powell's parents after Steven Powell was arrested on charges of voyeurism and child pornography in September 2011. Steven Powell has denied the charges.
A judge ruled earlier this month that Josh Powell could not have custody of his sons until he underwent a psycho-sexual evaluation.
Powell attacked his sons with a hatchet before igniting an explosion in his home last weekend, killing himself and his boys, officials have said. Powell locked a social worker out of the home before the explosion.