On Wednesday, Pappas was charged with the July 20 murder of Dr. Mark Hausknecht as he rode his bicycle to work in the Texas Medical Center.
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A law enforcement source tells Eyewitness News that Pappas once wore a badge himself.
According to records, Pappas served as a deputy constable in two precincts in Harris County.
His 12-year record as a peace officer began in May 1983 with the Precinct 2 Constable's Office, and ended with Precinct 7 in July 1995.
Pappas then spent 18 years between both precincts as a reserve officer. He ended his service in July 2013.
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During that time, our source says Pappas would have been around weapons and received firearms training.
As of Wednesday night, that skilled shooter is still on the run.
Anyone with information on Pappas' whereabouts is urged to contact the Houston Police Department Homicide Unit at 713-308-3600 or Crime Stoppers at 713-222-TIPS.
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