iStock/Thinkstock(HOUSTON) — The onetime doctor of former President George H.W. Bush was likely “targeted” when he was shot to death by a mystery gunman in Houston, police said on Thursday.Cardiologist Mark Hausknecht, 65, was killed on Friday in a residential neighborhood as he rode his bicycle.“There is a high probability the doctor was targeted,” Houston Police Chief Art Acevedo said in a statement posted Thursday on the department’s Twitter account. “No other information is available, as additional details are part of the ongoing investigation.”The latest twist in the shocking case came just days after police released images from the moment right before Hausknecht was gunned down as he rode his bicycle in Houston.The still images showed Hausknecht riding his bicycle as he crossed the busy intersection of Main Street and West Holcombe Boulevard in Southgate. The photos also showed the gunman behind the doctor just before the shooting.The suspect was riding a bike when he rode past the doctor and, “turned and fired two shots,” police said at a news conference Friday.Another still image showed the suspect, wearing a ball cap, headed west on Southgate Boulevard toward Travis Street.Houston police also released a composite sketch of the suspect on Saturday.Police said they are searching for a man who is about 30 years old and who was wearing a dark jacket when he fled the scene.Copyright © 2018, ABC Radio. All rights reserved.