HOUSTON – A man suspected of the slaying of a renowned cardiologist who was gunned down in the Texas Medical Center last month may have been seeking revenge for his mother, who died during surgery more than 20 years ago, authorities said Wednesday.

Houston Police Chief Art Acevedo said an arrest warrant has been issued for Joseph James Pappas II, 62, on a murder charge in the death of Dr. Mark Hausknecht. He is considered armed, dangerous and possibly suicidal, Acevedo said at a news conference Wednesday.

"There was a lot of planning that went into this. There was a lot of planning and, sadly, some skill," Acevedo said.

READ: Who is Joseph Pappas?

Acevedo said enhanced surveillance video released Monday in connection with the July 20 shooting death of Hausknecht led to a tip indicating Pappas' mother was a patient of Hausknecht's and she died during surgery more than 20 years ago.

Channel 2 Investigates learned Julia Pappas died of natural causes due to cardiovascular atherosclerotic disease, according to the Harris County Institute of Forensic Sciences.

WATCH: HPD announces murder charge against Joseph Pappas in shooting death of doctor in Med Center

Acevedo said Pappas hasn't been seen in 36 to 48 hours. He said the last anyone had heard from Pappas was in a Tuesday morning text message in which Pappas wrote that he was going to kill himself.

Officers conducted a welfare check at 9 p.m. Tuesday and did not find him there.

Police searched a residence in the 5000 block of Stillbrooke in Westbury early Wednesday morning. Pappas is listed as the owner of that home.

"We have plenty of evidence that ties him to this crime," Acevedo said, adding that evidence was removed from the home that tied Pappas to the crime. "We need to find this guy. If he's committed suicide, we need to find the body."

Investigators said Hausknecht was riding his bicycle along Main Street when he was shot three times by another cyclist, who then fled the scene. The bicycle used in the crime has not yet been recovered, Acevedo said. It is described as a 10-speed Schwinn bicycle.

Friends and family have 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.

BREAKING: @houstonpolice @ArtAcevedo says Joseph James Pappas is accused of killing Dr. Mark Hausknecht. HPD believes Pappas held a 20 year grudge. HPD says Dr. Hausknecht operated on Pappas' mother 20 years ago, she died while in surgery. @KPRC2 pic.twitter.com/XYnP5zrU10 — Sophia Beausoleil (@KPRC2SophiaB) August 1, 2018

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

In 2000, Hausknecht treated former President George H.W. Bush for an irregular heartbeat after the ex-president complained about lightheadedness.

On the website ARMSLIST.COM, which is a website that private citizens can sell weapons to other people, there are several listings where the contact phone number for the items is the same contact phone number for Pappas Realty.

Several items were listed for sale on July 25. Hausknecht was shot and killed July 20. It is not clear if any of the items for sale were used in the crime.

A photo of the listings and contact information are below:

Listings appear to have been posted by the man accused of shooting a Houston doctor to death.

Mayor Sylvester Turner released a statement Wednesday that read:

“The Houston Police Department’s identification of a suspect in the shooting death of Dr. Mark Hausknecht is more proof of the excellent results that come from HPD’s top notch investigators working with information provided by the public, from prominent cases to those that escape widespread attention.

"While each homicide is a tragedy for our community, I am thankful that last year’s Houston homicide count fell to a three-year low and that Chief Acevedo and his staff are using preventive approaches designed to reduce the count even further.

"Let us keep the family of Dr. Hausknecht in our prayers as they begin the long road to healing.

“While Houstonians can take comfort in the fact that we believe we know the identity of the suspected shooter, Joseph J. Pappas, he has not yet been located. I’m asking the public to continue to partner with police. Just as a tip led to his identity, we still need anyone with information on his whereabouts to come forward. They can call the HPD Homicide Division at 713-308-3600 or Crime Stoppers at 713-222-TIPS and they can remain anonymous.”