HOUSTON, Texas (KTRK) -- Police say Joseph Pappas was planning on killing Dr. Mark Hausknecht.
"I would call it, kind of like, the stalking of the doctor in terms of all the research he did on him," said Houston police Chief Art Acevedo.
Sources say Pappas had compiled a dossier on Dr. Hausknecht and he may have used his expertise in law enforcement to gain access to some of the information.
"This is a capable individual. He knew how to find out information. Remember, he had been a constable," Acevedo said.
In fact, sources say Pappas had been following Hausknecht since the beginning of July and say Pappas was seen following him at least five times in the weeks before the murder.
Investigators were able to gather surveillance videos that helped determine who Pappas was. Video of the murder itself was also captured by a METRO bus.
"We actually found the murder as it occurred, which is one of the most chilling videos I've ever watched. That's why when we saw the skill of that individual, we wanted to bring him into custody very quickly," Acevedo said.
Pappas was a skilled marksman, and Acevedo says the video showed that.
"He just never stopped. Never lost stride," Acevedo said.
Two weeks after the murder, after a call to police, officers found Pappas and approached him. That's when Acevedo says Pappas shot himself, but Acevedo says he seemed prepared for something else.
"When you have two guns on you, plus a bulletproof vest, body armor, that's not an indication that you're planning on killing yourself," said Acevedo.
"I'm convinced he was waiting for that officer to make a tactical error. I'm convinced had he made that tactical error instead of acting in a very safe manner, we'd have a dead cop," said Acevedo.
After countless hours of investigation, police say a dangerous man is no longer a threat to the community, as a doctor who saved so many lives is remembered for the life he led.
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Houston police Chief Art Acevedo reveals details on murder of Dr. Mark Hausknecht