JERSEY CITY, N.J. -- A gunman who killed a rookie officer responding to a report of an armed robbery at a drugstore early Sunday never tried to rob the store and instead lay in wait for police, telling a witness to watch the news, because he was "going to be famous," authorities said.

Lawrence Campbell shot officer Melvin Santiago in the head shortly after he and his partner arrived at the 24-hour Walgreens around 4 a.m., Jersey City Mayor Steven Fulop said. Other officers returned fire at Campbell, killing him.

Campbell, 27, of Jersey City was one of three suspects wanted by police in connection with another homicide, Fulop said.

Fulop said Campbell was carrying a knife when he walked into Walgreens and asked for directions to the greeting card aisle. He assaulted an armed security guard at the store and snatched his gun, Fulop said. Campbell waited for officers to arrive, then shot Santiago with what police believe was the guard's weapon.

"Today was a horrible day for Jersey City," Fulop said.

Dozens of officers stood single file at the entrance of the hospital and saluted as Santiago's flag-draped body was carried into an ambulance. A handful of younger officers consoled one another as they walked away. Santiago, 23, graduated from the Police Academy in December.

Fulop was there when Santiago's body arrived at the hospital. As Santiago's mother identified the body, Fulop said, she "just keep repeating the badge number and saying that it's not possible."

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 she 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 man began shooting, Belviso said.

"We thought he was running, coming toward us," said Belviso, 61, who was riding along with a friend. "He kept on shooting."

Bullets flew through the cruiser's windshield, 13 in all. The man 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 spokesman 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 said.

Police are searching for another man who they believe was involved in the previous homicide with Campbell, Fulop said. They have been seeking Daniel Wilson for the past three days, Fulop said.

The Jersey City Police Benevolent Association said in a statement that its members' 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."

Gary Nahrwold, 24, recalled his friend Santiago first saying a decade ago that he wanted to become a police officer. Nahrwold also hopes to join the force and said he won't be discouraged by Santiago's slaying.

"It just gives me more purpose to do it," he said. "I'm not going to be deterred by some senseless crimes."

Information for this article was contributed by Julio Cortez and Ashley Thomas of The Associated Press.

A Section on 07/14/2014