HOUSTON (CBSDFW.COM/AP) — Authorities in Houston have released a composite sketch of the man suspected of fatally shooting a cardiologist who once treated former President George H.W. Bush.

Dr. Mark Hausknecht was shot to death while riding his bicycle to work Friday morning at Texas Medical Center. Police have said the shooter rode past Hausknecht, then turned around and opened fire.

The suspect sketch released over the weekend depicts a man wearing glasses and a cap. Police have also released surveillance photos, taken from a distance, that appear to show the bicyclists crossing paths.

Authorities are investigating whether the killing was targeted or random.

Hausknecht treated Bush in February 2000 for an irregular heartbeat after the ex-president complained about lightheadedness while visiting Florida.

Mr. Bush said he was “deeply saddened” by Hausknecht’s death and sent his condolences to his family and colleagues.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)