Santiago is the first Jersey City officer killed in the line of duty since Detective Marc DiNardo died in July 2009 during a raid on an apartment while searching for suspects in a robbery.
"It is a tragic situation when any officer is killed in the line of duty," Fulop said. "Melvin was an officer who represented everything one would want to see in a police officer. I know the entire city's thoughts and prayers are with the Santiago family during this difficult time and we mourn together."
Jean Belviso, who has been delivering newspapers for 10 years, was driving through the Walgreens parking lot when she said saw a man wearing burgundy sweatpants and a baseball cap walk out of the store. A police cruiser pulled up in front of Walgreens, and the suspect began shooting, the 61-year-old Belviso said.
"We thought he was running, coming toward us," said Belviso, who was riding along with a friend. "He kept on shooting."
Bullets flew through the cruiser's windshield, 13 in all. The suspect was shot multiple times, and officers slapped handcuffs on him, Belviso said.
Campbell's body remained on the ground next to the bullet-riddled cruiser for more than five hours after the shooting before it was placed in a coroner's van and taken away.
Markeisha Marshall, a spokeswoman for Walgreens, said the company was "deeply regretful" over the officer's death and extended its sympathies to his family and friends. The store has round-the-clock armed security, Marshall noted.
Police are also searching for another man who they believe was involved in the previous homicide with Campbell, Fulop said. They have been aggressively seeking Daniel Wilson for the last three days, Fulop said.
The Jersey City Police Benevolent Association said in a statement that their hearts were heavy over Santiago's death.
"Patrolman Santiago knew the risks associated with this job, yet he put himself in front of danger in order to keep Jersey City safe," the association said. "Words cannot adequately express our feelings about this senseless tragedy."
The officer's stepfather, Alex McBride, said Santiago was "very proud" to be a police officer, following in the footsteps of his uncle. McBride said he had been in Santiago's life for 14 years, noting that his stepson had wanted to be a police officer since playing the "Call of Duty" video game.
"Melvin was the best kid," he said, choking up as he sat hunched over on a plastic crate in an alley outside the family's apartment. "I watched him graduate from high school. He joined every sport, everything. He never did no harm to nobody. And he was full of life."
He continued: "There was something about his smile. He had that terrific smile."