CHICAGO, Illinois (CNN) -- One of the suspects accused of killing an honor student in a beating captured on tape in Chicago has admitted to jumping on the victim's head after he was already lying on the ground, said a spokeswoman for the Cook County state's attorney.

Derrion Albert, 16, was beaten to death last week. His death was captured on video.

In the videotaped confession, 19-year-old Silvanus Shannon also said that the victim, Derrion Albert, 16, never struck him, said the spokeswoman, Tandra Simonton.

Three teens arrested in Albert's death -- Silvanus Shannon, 19; Eric Carson, 16; and Eugene Riley, 18 -- were seen on the videotape attacking Albert, and were charged with first degree murder and held without bail, Simonton said. Monday night authorities said they charged a fourth suspect, 17-year-old Eugene Bailey, with murder.

On Monday during the bond hearing, prosecutors described how the street fight escalated from a dispute between two factions at Albert's high school to a beating that left the honor student dead.

Prosecutors said Albert was an "innocent bystander" who ended up in the middle of a street fight between two factions of students at his school, Christian Fenger Academy High school, on Chicago's South Side.

When school let out at 2:50 p.m. on Thursday, Albert was on his way to the bus stop when two groups of students converged on the street, Simonton said.

AC 360 Anderson Cooper has the latest on the beating death of a Chicago honors student on "AC 360."

Tonight, 10pm ET see full schedule »

The two factions, one that lived near the Altgeld Gardens housing development and one in an area known as "The Ville," began fighting after a shooting earlier that day that police called gang-related.

Albert was approached by Eric Carson and another unknown person, both members of the "The Ville" faction, Simonton said. Carson struck Albert in the head with a piece of a wooden railroad tie, and the second person punched him in the face, Simonton said.

Albert was knocked unconscious by the blows for a short period, Simonton said, but gained consciousness and quickly tried to move from the escalating street fight.

"He gained consciousness and moved a few feet away, but as he was trying to get up, he was attacked by a second group," Simonton said.

That group, made up of five members from the opposing faction, then took their shots at Albert, Simonton said.

He was struck in the head by Riley with the piece of railroad tie, a rectangular piece of wood used as a base for railroad tracks, Simonton said.

Once Albert was on the ground again, Shannon was seen "stomping on his head repeatedly," Simonton said.

An amateur videotape shot by a witness, which has been broadcast nationally, showed the attack unfolding. A local TV station that received the tape turned it over to police. Watch graphic video of the attack »

The video shows that, as the attackers ran away, the person with the camera and several others approached Albert and carried him into a nearby building.

"Derrion, get up!" a female voice pleads on the video.

Albert was taken to Roseland Community Hospital and then to Advocate Christ Hospital and Medical Center, where he was pronounced dead, Simonton said.

Shannon and Riley do not have criminal records. Carson is on probation for a 2008 robbery conviction, according to Simonton.

On Monday, family and friends, some wearing shirts bearing Albert's photo, held a vigil in his honor.

Albert's grandfather, Joseph Walker, told CNN affiliate WLS-TV that his grandson was a good kid who didn't deserve to die.

"He was in Bible class this Tuesday night. Church on Sunday," Walker told WLS-TV. "I have no trouble out of my grandson whatsoever. This thing that happened to him is so horrific that we just don't know what we're going to do. We lost a really dear friend in my grandson. He was a blessed child."

Walker said the family was struggling to come to terms with why Albert was killed.

"I don't know where all this anger come from these people today," he told WLS-TV. "That's just too much anger for someone to have in their heart. All I can do is I'm going to pray for these people, I'm going to to pray for forgiveness." Rick Sanchez asks, "Are our young people salvageable?" »

Albert's aunt, Rose Braxton, told CNN affiliate WGN-TV that the family was hurt again when a memorial in Albert's honor was burned down.

"To go and burn a memorial after such tragedy, then that just speaks for itself to what kind of people they are," she told WGN-TV.

Family and friends asked the community to turn in anyone they knew who was a part of Albert's beating.

"What kind of person, what kind of individual, has such rage and such anger and such madness?" the Rev. Michael Pfleger said. "We've got to get to the hearts of our children, because nothing, nothing, excuses or justifies the actions of an individual who would beat another individual. Nothing justifies that in this society. "

Pfleger said it was time to make a change, so children aren't afraid to go to or from school.

He said this kind of teen violence was not just an issue for Chicago, but from "Oakland to Newark."

Ron Huberman, CEO of Chicago Public Schools, said he had met with Albert's classmates.

"How do we make sure this event doesn't become another event?" he said. "Another vigil on another day."

Huberman said he will fight every day to ensure the safety of children in Chicago's schools.

"We can promise them and we can say that we we will absolutely remember Derrion," he said.

Flanked by people holding signs with photos of a young child and the words "Don't shoot, I want to grow up," Pfleger pleaded for peace.

"It's time for guns, and it's time for two-by-fours to stop being the way we treat each other," he said.

All About Chicago • Murder and Homicide