Surveillance footage has been released in the death of renowned Texas cardiologist Dr. Mark Hausknecht in hopes of identifying the suspect.
Dr. Hausknecht, who treated President George H.W. Bush, was gunned down by another man, who was also riding a bike.
A surveillance camera aboard a bus in Houston captured video of the doctor crossing an intersection over the weekend.
As the doctor goes out of frame, his suspected killer comes into view about half a block behind him.
Another video shows the doctor in his blue scrubs as he cycles to work. The alleged killer is now much closer. Moments later, the doctor was shot dead.
The suspect rode past the doctor, turned and fired two shots, according to cops. The doctor immediately went down.
Security expert Pat Brosnan, a former NYPD detective, analyzed the videos for Inside Edition.
"Let's be crystal clear, this is 1,000-percent personal," he said. "He could have shot him in the back and been guaranteed anonymity because he was riding up behind him. Instead, he elected to go in front of him, pivot, and shoot him in the front — that speaks volumes."
KTRK-TV reporter Marla Carter has been covering the story for her outlet. She said the suspect may be from the area because of how easily he was able to get away from the scene.
The suspect in the video is wearing a khaki baseball cap a blue short-sleeved polo shirt, tan shorts and an olive green backpack.
Police also released a sketch of the suspect, described as being about 30 years old, 5 foot, 10 inches, and described as "thin but fit.”
Friends and neighbors of the doctor have joined the hunt, going house-to-house in search of witnesses.
Bush was among those expressing his horror at the murder, saying in a statement: "Mark was a fantastic cardiologist and a good man. I will always be grateful for his exceptional compassionate care."
Bush was treated by the doctor 18 years ago.