A police officer shot in the head by a doughnut shop robber died Thursday morning, the police commissioner announced.

The 54-year-old officer, Charles Cassidy, died at 9:40 a.m. at Albert Einstein Medical Center, police Commissioner Sylvester Johnson said.

He is the second Philadelphia officer in 18 months to be murdered. He was the third city officer shot in the span of four days.

"This is a sad day for the city of Philadelphia," Johnson said. "This is a sad day for the Philadelphia police department."

Cassidy, a 25-year police veteran, was shot in the forehead as he walked into a Dunkin' Donuts shop at around 10:30 a.m Wednesday.

Police released portions of a chilling videotape that shows the hooded robber pushing aside two customers and waving a gun as he approaches the counter. It also shows him grabbing the fallen officer's pistol as he fled.

The search for the suspect continued Thursday morning.

"We still have an armed and dangerous man out there in the streets of Philadelphia," Johnson said.

Mayor John Street said the city would devote whatever resources are needed to catch the killer.

"We will not allow this crime to go unpunished," he said.

A prayer service was scheduled for 10 a.m. Friday at City Hall.

The video showed the gunman running through the shop's parking lot in what Johnson described as a distinctive gait, almost as if he had a limp. Footage of the actual shooting was not made public.

The gunman went into the shop and demanded money just before Cassidy opened the door, said Sandra Kim, a Dunkin' Donuts employee who was behind the counter at the time. He then spun around and shot the officer as he held the door.

Cassidy was a regular customer who came in twice a day for a large coffee with cream and sugar, Kim said. "He's always nice to all the employees," she said. "The officer was just coming in for a cup of coffee like normal."

Johnson said the officer was doing a routine check on the shop, which had been robbed Sept. 18, possibly by the same man. He said he didn't think the robber got away with any money Wednesday.

The shooting came about 12 hours after a masked gunman shot Traffic Officer Mariano "Mario" Santiago in the shoulder during a chase downtown. He survived.

Early Sunday, an officer responding to a melee at a West Philadelphia nightclub was shot in the ankle.

On Sept. 24, a suspect jumped out of a car during a traffic stop and shot a rookie officer in the face at close range with a sawed-off shotgun. The officer needed reconstructive surgery, but was released from the hospital about a week later.

In May 2006, Officer Gary Skerski was fatally shot in the neck when a man robbing a bar fired a shotgun out the back door. The killer, Solomon Montgomery, pleaded guilty to first-degree murder and was sentenced to life in prison on Tuesday.

Philadelphia has faced an uptick of gun violence recently, with more than 400 people murdered in the city in 2006 — the highest total in nearly a decade. This year's pace is nearly identical.