Houston police were on the lookout Aug. 1 for Joseph James Pappas, 62, suspected of killing one of former President George H.W. Bush’s doctors in apparent revenge for the death of his mother who died on the cardiologist’s operating table more than 20 years ago, officials said.

Police Chief Art Acevedo said Pappas should be considered armed, dangerous and possibly suicidal. A tip led police to suspect Pappas, he added, but wouldn’t reveal any more information

“There was a lot of planning that went into this. There was a lot of planning and, sadly, some skill,” Acevedo said of the July 20 attack on Dr. Mark Hausknecht, who was gunned down while riding his bike to work at Houston Methodist Hospital, which is part of the busy Texas Medical Center. Video showed the shooter, believed to be Pappas, riding past Hausknecht on a bicycle before turning around and firing.

Acevedo said the last anyone had heard from Pappas was in a July 31 morning text message in which the suspect wrote that he was going to kill himself and when police searched his home they found evidence tying him to the killing.

The chief said Pappas is white and very fit, and likely getting around on his 10-speed bicycle, which he rides “extensively and almost exclusively.”

Friends and family described Hausknecht as a humble and generous man who was adored by his patients, volunteered in his community and cared about the environment.

Hausknecht was also an avid cyclist and rode his bike to work each morning, as he lived less than 2 miles (3.2 kilometers) from his office.

Police were able to identify Pappas, “thanks to the fact that we have a community that’s cooperative, that is a partner, that understands that they have a responsibility to play a huge role in keeping our neighborhoods safe,” the chief said, NBC News reported.

Acevedo explained that residents close to the shooting examined their home security video, and police were able to obtain an image that led to Pappas’ identification through additional tips.

(Material from the Associated Press was used in this report)