Vegas Killer Was 'Thrill-Seeker' Gambling as Much as $10,000 a Day, Expert Says

His father, Benjamin, was described as "psychopathic" and "suicidal" when was placed on the FBI's most wanted list in the 1960s.

The gunman who opened fire in Las Vegas over the weekend was an avid gambler and an adrenaline junkie, an expert tells Inside Edition.

“We know that he was a thrill-seeker, a gambler, a high-roller," criminologist Dr. Jordan Casey told Inside Edition, responding to reports that Stephen Paddock was gambling up to $10,000 a day before this weekend’s massacre that killed 59 people and wounded more than 500.

“It’s possible, for the gambling, the thrill was gone and he needed something to feel alive again,” Casey said.

Meanwhile, more details about Paddock’s past have also come to light.

He was on the high school tennis team in Sun Valley, Calif.

His father, Benjamin, was described as “psychopathic” and “suicidal” when was placed on the FBI’s most wanted list in the 1960s.

The elder Paddock was convicted in 1961 of robbing two banks in Arizona, making off with $25,000. He was sentenced to 20 years in federal prison when Stephen Paddock was 8.

He escaped in 1968 and ultimately settled in Oregon under an assumed name.

A 1987 video shows the elder Paddock ranting at reporters after he was arrested for allegedly running an illegal bingo parlor in Oregon. He was arrested by federal agents and returned to prison for a year.

He died in 1998 in Texas.

At a press conference late Tuesday, authorities in Las Vegas said Stephen Paddock’s girlfriend, Marilou Danley, is now a person of interest.

She was traveling in Asia on Sunday, when the shootings occurred, officials said.

She is now returning from Tokyo. A NBC report said she was in the Philippines when Paddock wired $100,000 to the country.

Watch: Hear How SWAT Team Closed in on Las Vegas Gunman in His Hotel Room