It is believed that Joseph James Pappas spent years planning the murder following the death of his mother on Dr. Mark Hausknecht's operating table.
Could the bike used in the cold-blooded daytime murder of President George H. W. Bush’s former doctor lead cops to the killer?
Houston Police Chief Art Acevedo is asking for the public's help to locate 62-year-old real estate agent Joseph James Pappas, who is suspected of killing cardiologist Mark Hausknecht on July 20.
Pappas most recently worked as a reserve officer in Harris County, Texas, from 1995 to 2013, according to the station. He was also a deputy constable from 1983 to 1995.
“There was a lot of planning that went in to this murder and sadly, some skill,” Acevedo said.
Cops say Pappas' distinctive 10-speed bike he was riding on the day of the shooting may be the key to catching him.
“The bike has not been recovered," Acevedo said. "That was his primary means of transportation on a daily basis, according to many witnesses we have talked to."
Inside Edition spoke to Alain Guillerme of Al's Cycle Solutions in New York about the bicycle. He said it is a "classic Schwinn."
"I can tell, it is an older Schwinn," he said. "This bike was probably made in the early 80s, late 70s."
When looking at images of the suspect's bike, he said it was a steel bicycle which "makes the tube really thin," adding that "the bikes today have fatter tubes because they are made out of aluminum."
The bike isn't the only indication that Pappas may be living in the past. He lived his entire life in the house he grew up in and police say revenge drove him to kill.
Pappas' mother died on the doctor's operating table more than 20 years ago, according to police.
Forensic Psychiatrist Dr. Keith Ablow explained to Inside Edition how someone could hold a grudge for so long.
"He is almost lost in the past," Dr. Ablow said. "He is riding this old bike. When he loses one of those people, it could be that all he has left is the story of that loss and it becomes convoluted and very dark and then he feels like he needs to take revenge."
Police say Pappas seemed to be wrapping things up in the final hours before the murder. He signed over the deed to his house to a woman from Ohio and called a courier, Joe Donaldson, to pick up the document.
"The day I picked up the documents he seemed paranoid," Donaldson recalled to Inside Edition. "He seemed nervous. He was looking up and down the street like someone was coming to get him."
He had also placed online ads selling thousands of dollars’ worth of firearms.
Police say they have reason to believe Pappas is suicidal.
Police in Houston stress that the suspect has extensive knowledge of handguns and should be considered armed and dangerous.