After an early-morning sweep, police arrested four Simon Gratz High School students in connection with last week's deadly beating of Starbucks manager Sean P. Conroy on a subway concourse, an assault that left commuters and Center City residents worried about their safety and others searching for a motive.

During questioning yesterday, the four suspects offered much the same story as the one given by another Gratz High teen who was arrested shortly after the March 26 assault: They were just fooling around and never intended to kill Conroy, just sucker-punch him.

None of the teens accepted responsibility for the initial blow that knocked Conroy to the ground or admitted delivering any fatal punches or kicks as he pleaded for help. They had gone after Conroy on a whim, police said, and were trying to do a "body drop," that is to knock him out with one blow.

Homicide Capt. Mike Costello said it remained a "senseless" crime that he could not explain. Police ruled out robbery as a motive because nothing was taken from Conroy.

News of the arrests was welcomed by Conroy's father, Steve, who said he desperately wanted to see those responsible apprehended.

"We wanted something to happen," he said. He had buried his son on Tuesday, days after the investigation appeared to have hit a standstill. "All of a sudden there is movement where there was no movement."

He said he would never make sense of his son's death.

Charged yesterday with murder and conspiracy were: Ameer Best, 17, of the 2000 block of North 24th Street; Arthur Alston, 16, of the 800 block of Fisher Avenue; Rasheem Bell, 16, of the 4700 block of Tampa Street; and Nashir Fisher, 16, of the 3500 block of North Marvine Street. The four will likely be arraigned today.

Last week, police arrested Gratz student Kinta Stanton, 16, of the 4900 block of North Smedley Street in Logan, as he was fleeing the scene. He also has been charged with murder and conspiracy.

Costello said there may be a sixth teenager involved. Detectives have not confirmed that or identified that person.

Detectives had identified the suspects last week but said they were keeping a close watch on them while trying to build a tight case.

"It's one thing to know, it's another thing to prove it," Costello said, detailing how authorities were chasing leads and confirming information before yesterday's sweep.

The attack, on a Wednesday afternoon on a crowded subway platform, shocked many. Philadelphia, which has struggled with violent crime, had had a drop in assaults and homicides during the last six months, and Center City is considered one of the safest areas.

In his statement to police, Stanton said that on March 26 he and his friends cut school and were hanging around Center City when they decided to go after Conroy, who was walking on the concourse at 13th and Market. The victim had been on his way to work at the Starbucks in the Philadelphia Marriott Downtown.

Conroy was jumped about 2:35 p.m. A SEPTA officer witnessed part of the attack and rushed to help Conroy, including performing CPR until medics arrived. The teens ran when they saw the officer approaching.

Conroy lost consciousness and died at Thomas Jefferson University Hospital within an hour of the attack.

The medical examiner ruled the death a homicide, saying that the beating triggered a fatal asthma attack.

Three of the teens were picked up at the high school; the fourth student was late to school and was apprehended en route, police said.

Outside Gratz yesterday afternoon, four students said they noticed the commotion as one officer in uniform and several others in plainclothes came into the school to make the arrests.

A youth who would give his name only as Ty said he was walking into school when a teacher called out, "Turn around!" Ty stopped on stairs and stepped back as a procession of police went past. He could tell they had someone in custody, but he couldn't tell who.

"I've never seen no cop come into the school and take somebody out," he said yesterday, wondering which of his classmates had been arrested. "We probably know every last one of them."

Ty, 15, said he was interested to know whether the youth already in custody had identified the other alleged killers.

"Me personally, the way I was raised, I wouldn't snitch," he said.

Last night on the 2400 block of North 24th Street, the address authorities gave for Ameer Best, one neighbor said the family had recently moved out. She said she didn't know where they were now.

On the 3500 block of North Marvine, the address given for Nashir Fisher, several neighbors said they didn't recognize the name.

The door at the home of 16-year-old Arthur Alston, in the 800 block of West Fisher Avenue, was answered by a man with a gray-flecked beard and wide-brimmed hat who said he was the boy's grandfather. Visible inside the two-story rowhouse were two children who looked to be no older than middle-school age and another man.

"Nobody wants to talk," said the grandfather, who did not give his name.

There are about 100 severely dilapidated rowhouses in the 4700 block of Tampa Street, where 16-year-old Rasheem Bell lives. The street curves sharply in the middle and backs onto a railroad. No one was out and it was impossible to determine which house was Bell's.

The four suspects were all in custody before noon, but detectives said that because they were minors, authorities could not question them until their parents or guardians had been brought to headquarters.

Once they started talking, the story was virtually the same as the story Stanton told detectives last week.

About nine hours after the teens were taken into custody, the District Attorney's Office approved the charges.

Remembered as a quiet, generous man, Conroy grew up in Upper Darby, lived in California for several years, then returned to the region and settled in South Philadelphia. Three days before he was killed, he had become engaged to be married.

Inquirer staff writers Dwight Ott and Michael Matza contributed to this article.