A rare form of blood cancer is responsible for the death of an NYPD chief who is believed to have gotten the disease while acting as a first responder at Ground Zero following the Sept. 11 terrorist attacks.

Steven Bonano, 53, died on Saturday at Memorial Sloan Kettering Cancer Center with friends and family at his bedside, New York Daily News reported. Since 9/11, more than 900 first responders have died of ailments linked to their service at Ground Zero.

"He loved the police department, it was his life," a colleague told the New York Post. "He was a cop's cop. He was my mentor. He was always looking for us to do better. He always did better for himself. He accomplished so much."

At the time of the terrorist attacks, the 30-year veteran was commander of the NYPD's elite Emergency Service Unit. As he went onto participate in the rescue and recovery efforts at the World Trade Center site in the weeks following the terrorist attacks, he might have contracted cancer as a result of inhaling toxic materials.

In 2012, he became the head of security at the Barclays Center venue in Brooklyn, which hosted a bone-marrow registry in 2013 to help prolong his life.

"Bonano was a true leader not because of rank but because of the man he was," said Dennis Gonzalez of the NYPD Hispanic Society, which Bonano was a member of. "Those who knew him as a police officer knew he was destined for greatness."

Although his tragic death is believed to be linked to his time at Ground Zero, the NYPD declined to make comments, according to UK MailOnline.

Meanwhile, cancer among 9/11 responders is 15 percent higher than that among people not exposed to the Ground Zero toxins, according to a recent study by Mount Sinai Medical Center's World Trade Center Health Program. Three types of disease have primarily seen an increase, including blood cancers such as leukemia and lymphoma.

Awarded the Police Combat Cross, the department's second-highest honor, the Bronx-born Bonano also earned a pilot's license and a Master's degree from Harvard University during his time on the force.