(CNN) A man whose mother died during surgery 20 years ago is the suspect in the fatal shooting of a prominent Houston cardiologist who performed the operation, police said Wednesday.

Chief Art Acevedo said the mother of Joseph James Pappas, 62, was a patient of Dr. Mark Hausknecht , who was fatally shot as he rode his bicycle to work at Houston Methodist Hospital on July 20. Police earlier said Pappas was born in 1953.

Houston Police released a photo of Joseph James Pappas, who is a suspect in the death of Dr. Mark Hausknecht.

"So, it appears that this may be a 20-year-old grudge that this man held," Acevedo told reporters.

CNN called a phone number listed for Pappas' real estate company on Wednesday, but the call went to voice mail.

That phone number also is linked to recent listings on a firearms auction website for several guns, ammunition, tactical vests and ballistic plates for car doors. The posts, from a user in Houston, apparently went online days after Hausknecht was shot.

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