An Australian investment banker who admitted chaining a fake bomb to a teenager was reeling from the breakdown of his marriage, drinking heavily and exhibiting wild mood swings in the years before the bizarre extortion attempt, his ex-wife and a psychiatrist said Friday at his sentencing hearing.

But Deborah Peters testified she has no idea why Paul Douglas Peters committed the crime. "I don't know if even Paul knows why he did it," she said.

The 51-year-old faces up to 20 years in prison for tethering a bomb-like device to the neck of then-18-year-old Madeleine Pulver in August 2011 while she was alone in her family's Sydney mansion. In March, he pleaded guilty to aggravated break and enter and committing a serious indictable offense.

It took a bomb squad 10 hours to remove the device, but it contained no explosives and Pulver was not injured. Peters, who wore a rainbow-striped ski mask and wielded a baseball bat in the attack, left a ransom note with an email address that helped authorities track him down.

Peters, who traveled frequently between the United States and Australia on business, fled to the U.S. and was arrested nearly two weeks later at the Louisville, Kentucky, home of his former wife, Deborah Peters. He was extradited to Australia and has remained in prison since.

Deborah Peters wept in New South Wales state District Court on Friday as she described how her then-husband's behavior began to change in 2000.

"Paul started to disconnect," she told the court. "I didn't know who was going to walk through the door. ... One minute he'd be OK; the next minute he'd be upset or angry."

The mood swings coincided with his attempt to write a book, she said. Initially, it was meant to be about a man who finds a key and looks for treasure, she said, but it ended up being much darker, about a villain who kidnapped someone and addicted the victim to drugs.

Peters was determined to finish the novel and was spending hours in the basement working on it, she said. He also began drinking more: up to two bottles of wine and two large gin and tonics with dinner every night, she said.

Deborah Peters testified that she divorced her husband in 2007, after he refused her pleas to get help, but they remained close.

In Feb. 2011, they tried to reconcile. But Peters' behavior grew more erratic, and in May 2011, he threw a fit during their daughter's 16th birthday dinner, Deborah Peters said. She promptly kicked him out.

Psychiatrist Bruce Westmore, testifying for the defense, said Paul Peters was "angry and revengeful" over his failed relationship and separation from his three daughters, was obsessed with his book and may have tried to become the vengeful character in the novel.

Westmore said he believes Peters suffers from depression, but was not psychotic and had an awareness of what he was doing at the time of the crime. Since his arrest, Peters has told the psychiatrist that he has no memory of the attack and described his own actions as "bizarre," ''absurd" and "stupid." But Peters is so complex, pinpointing an exact diagnosis is difficult, Westmore acknowledged.

"I've never met anyone like Mr. Peters before," Westmore said.

Peters, wearing a suit and looking thinner than he did at the time of his arrest, nodded briefly in the direction of his victim's parents, Bill and Belinda Pulver, who sat in the front row of the public gallery. Bill Pulver stared back at him, stone-faced.

It was the first time the two men have come face-to-face. Outside court, Bill Pulver said he found the testimony on Peters' mental state interesting, but ultimately thinks the attack was all about money.

"He threatened our daughter with a baseball bat ... We have no question in our mind what this was all about," Pulver said. "We believe it was clearly an extortion."

Why Peters targeted the wealthy Pulver family has yet to be explained. U.S. court documents show Peters once worked for a company with links to Bill Pulver, but the family says they don't know him and remain confused as to why Madeleine was attacked.

The hearing was adjourned until Oct. 31.