Surveillance images show gunman behind George H.W. Bush's former doctor moments before murder

Houston police released surveillance images Sunday showing a gunman trailing behind George H.W. Bush’s former cardiologist moments before the doctor was shot and killed while biking to work — clues authorities hope will help nab the killer.

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Dr. Mark Hausknecht, circled in green, riding his bike Friday morning.  (Houston Police)

The images taken from surveillance cameras in the area show Dr. Mark Hausknecht biking across an intersection while a man trails behind and eventually approaches him. Police said Hausknecht was shot and killed moments later, about one block away.

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The gunman, circled in red, is seen approaching Hausknecht from behind.  (Houston Police)

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The gunman rides closely behind Hausknecht about a block away from where the doctor was shot and killed.  (Houston Police)

Another image shows a man heading west on Southgate Boulevard and Travis Street shortly after the deadly shooting.

The images comes a day after police released a sketch of a man they believe is the gunman. Authorities are also offering a $5,000 reward for information leading to an arrest.

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The suspect moments after the shooting.  (Houston Police)

SKETCH RELEASED OF SUSPECT SOUGHT IN MURDER OF GEORGE H.W. BUSH'S FORMER DOCTOR

The 65-year-old doctor was heading to work at the Texas Medical Center when he was shot at least twice at 9 a.m. Friday, police said. Hausknecht dropped to the ground immediately while the gunman fled the scene on a light-colored mountain bike, police said. 

Witnesses told police the shooter was a clean-shaven man who is about 30 years old, 5-foot-10 with a slender build. He was wearing a baseball cap, sunglasses, a gray warmup jacket and khaki shorts the morning of the shooting.

It’s still unclear if Hausknecht’s death was a random or targeted attack, the Houston Chronicle reported.

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Police released a sketch of the shooter accused of killing Dr. Mark Hausknecht on Friday. (Houston Police)

"This is a crime that doesn't make sense," Houston Police Chief Art Acevedo said Saturday. "We don't even have a motive yet."

Hausknecht was a well-known doctor who had been in medical practice for almost 40 years. He specialized in cardiovascular disease, said Marc Boom, president and CEO of Houston Methodist Hospital.

Dr. Neal Kleiman, who was a close friend of Hausknecht and worked at Houston Methodist Hospital, told “FOX & Friends” on Sunday the cardiologist was “in many ways a role model.”

“Emotionally it’s a very tough thing to deal with. I think we all experience that in the medical community. And this is completely…out of the blue. The medical center is generally regarded to be an almost protected environment,” Kleiman said about Hausknecht’s death.

FILE - In this Feb. 25, 2000, file photo, former President George H.W. Bush waves as he leaves Methodist Hospital with his cardiologist, Mark Hausknecht, after a news conference in Houston. Hausknecht, who once treated former President George H.W. Bush, was fatally shot by a fellow bicyclist Friday, July 20, 2018, while riding through a Houston medical complex, and police were trying to determine if the shooting was random or a targeted act. (AP Photo/David J. Phillip, File)

Hausknecht was a well-known doctor who once treated former President George H.W. Bush. (AP)  (AP)

In 2000, Hausknecht treated Bush for an irregular heartbeat. Bush said in a statement that Hausknecht was a “fantastic cardiologist and a good man.”

Katherine Lam is a breaking and trending news digital producer for Fox News. Follow her on Twitter at @bykatherinelam