HOUSTON (AP) — Friends and neighbors of a Houston man accused of killing one of former President George H.W. Bush's doctors said that much of the suspect's life was a mystery to them, describing him as respectful and polite, but withdrawn.

State records show Joseph James Pappas had worked in law enforcement for more than 30 years and was also a licensed real estate agent.

The search continued Thursday for Pappas, who's described by authorities as armed, dangerous and possibly suicidal.

Houston police said they're also looking into whether Pappas tried to sell various weapons online several days after the July 20 fatal shooting of Dr. Mark Hausknecht.

Police allege Pappas shot Hausknecht while the cardiologist rode his bike to work at Houston Methodist Hospital.

Houston Police Chief Art Acevedo said Wednesday Pappas might have been seeking revenge for his mother, who died on the doctor's operating table more than 20 years ago, in April 1997.

Houston Methodist Hospital was not aware of any previous threats that had been made against Hausknecht, said spokeswoman Stefanie Asin. Any such substantiated threats are reported to law enforcement, she said.

No disciplinary action had ever been taken against Hausknecht, according to the Texas Medical Board.

Hausknecht was shot three times while he was on his bike and Acevedo said the shots that Pappas is accused of firing as he also rode on a bike "took some skill."

Pappas had worked from 1983 through 1995 as a peace officer with two Houston-area constable offices. He also worked from 1995 through 2013 as a reserve officer for these same constable offices, according to records from the Texas Commission on Law Enforcement.

His father, Joseph James Pappas Sr., also worked as a peace and reserve officer for these same constable offices for more than 26 years. The elder Pappas was also an Army colonel, having served in WWII, and had worked as an attorney, according to his obituary.

Pappas' father died in 2010.

"The whole thing about Joey is amazing. I'm stunned," said Kathy Bilinosky, whose father was good friends with the elder Pappas.

Bilinosky, who grew up on the street behind the Pappas home in southwest Houston, said the younger Pappas was respectful but she didn't spend much time with him or his sister.

"They didn't go bike riding with us or any of that stuff," said Bilinosky, 63, who now lives in Bryan, Texas. "They more stayed home than most of the kids on the block."

Bilinosky said that in 1997, Pappas' mother, Julia Alice Walker, had gone into surgery and died unexpectedly.

Neighbor Jim Herd said the death of Pappas' mother "hit him hard." But he doesn't remember hearing Pappas speak bitterly about his mother's death.

Herd and Bilinosky said they didn't know what Pappas currently did for a living.

Pappas was licensed as a real estate broker and had a business called "Pappas Realty Company," according to the Texas Real Estate Commission.

The company had an address listed in an office building across the street from Houston's high-end Galleria mall. But the building's management on Thursday didn't have any records showing Pappas as a current or former tenant.

Herd said he knew that Pappas collected firearms.

On Armslist.com, a website where people can sell firearms, someone with the same phone number as Pappas' real estate company had several listings for a variety of weapons and accessories, including a .38-caliber revolver, a semi-automatic rifle and some bullet-proof vests.

"We're aware of it and we're looking into it," Houston police spokesman Victor Senties said regarding the listings on the web site.

Bilinosky said as the search continues for Pappas, she hopes that nobody else is hurt.

"If I could talk to Joey, I would say, 'We still love you sweetie,'" she said. "It's just such a shock."

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Follow Juan A. Lozano on Twitter at www.twitter.com/juanlozano70