The suspect in the murder of a cardiologist who treated former President George H.W. Bush committed suicide Friday as police officers confronted him.

What happened?

A manhunt for Joseph James Pappas had been ongoing since Tuesday. As authorities approached the suspect near his home, the man fatally shot himself, according to authorities. He was wearing body armor under his shirt when he died.

Pappas was suspected of killing Dr. Mark Hausknecht on July 20 in what investigators believe was a targeted attack. Hausknecht was shot three times by another cyclist while riding his bike to work in Houston.

Law enforcement said Pappas might have carried out the shooting as an act of revenge. Hausknecht, 65, was the cardiologist who treated Pappas' mother, who passed away unexpectedly on the doctor's operating table more than 20 years ago.

While Pappas was on the loose, Houston Police Chief Art Acevedo warned the public that the suspect was armed and dangerous and that text messages showed that he might be suicidal. Pappas was a gun collector and expert marksman with 30 years of law enforcement experience.

Did the suspect have a hit list?

An anonymous source reportedly claimed that Pappas might have had a hit list of other people he had planned to kill.

Described as a former friend of the suspect, the source reached out to KHOU-TV and said, "I personally do not think the doctor is the only person that [Pappas] is going to target. I think [Hausknecht] was number one on the list. And Joe is extremely intelligent. He's patient, he's unassuming, he's a deadly shooter."

The friend told KHOU, "[We were] hanging out together, over burgers and tacos, telling stories, and he mentioned being called the 'Greek shrimp' in high school and 'karma's a real b***h,' and one day the people who bullied him in high school would meet a day of reckoning."

"[Pappas] made the comment, at the time I thought it was a joke, 'Hey, don't worry you're not on my list.' Now looking back on it, it makes me queasy to think, 'Oh wait, maybe this guy has a list,'" the source said.

Houston police said they are unable to comment about whether Pappas might have a hit list. But Pappas' former friend warned, "If there's a bully he had in high school, I would tell that person to take an unplanned vacation to Alaska."

What else?

Hausknecht was a cardiologist at Houston Methodist Hospital and had treated former President Bush, 94. Houston Methodist Hospital said Hausknecht has been in practice for almost four decades and was an important member of the hospital staff.