UPDATE: Four teenagers have been charged with first-degree murder in Derrion Albert's beating death.
Silvanus Shannon, 19, Eugene Riley, 18, and Eric Carson, 16, all of Chicago, were charged as adults ordered held without bond. Eugene Bailey, 18, was also charged with first-degree murder and will appear in court Tuesday.
Prosecutors declared Albert an "innocent bystander" in the fight that led to his death.
Scroll down for more on the charges and video of the brawl.
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Chicago police are still investigating the gang fight that erupted Thursday in Roseland that resulted in the death of 16-year-old Fenger High School student Derrion Albert.
Albert was killed in a melee near the school that police believe is a continuation of ongoing tensions between Fenger students that are members of rival gangs.
An amateur video of the brawl shows dozens of people punching, kicking and swinging wooden boards in the street. Albert was struck by blows from one of those boards, Fox Chicago reports, and the video obtained by Fox shows a person getting hit with a board and then stomped on after falling to the ground.
As people rush to help the injured person, a voice can be heard on the video yelling, "Derrion, get up!"
Watch the footage (WARNING: GRAPHIC VIOLENCE):
Albert's mom said witnesses told her that her son "trying to help another student and kind of got mixed in with the crowd of the fight and he was hit."
A memorial and march planned for Sunday was rescheduled for Monday at 1 p.m., the Tribune reports.
UPDATE: Police are questioning four people in connection with Albert's death, Fox Chicago reported late Sunday night.
The student who hit Albert with a board is in custody, Fox reports, as police try to figure out why Albert, an honor student whom family and friends said was not involved with a gang, was killed.
Meanwhile, police beefed up security around Fenger Monday as students returned to school the week after the melee that led to Albert's death.
"We want to provide reassurance to the public that there's a police presence and they can feel safe in the neighborhood and kids can feel safe at school," the Tribune quoted Morgan Park District Commander Michael Kuemmeth as saying.
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The full story on the charges, by the AP's Karen Hawkins:
CHICAGO - Cell phone footage showing a group of teens viciously kicking and striking a 16-year-old honors student with splintered railroad ties has ramped up pressure on Chicago officials to address chronic violence that has led to dozens of deaths of city teens each year.
The graphic video of the afternoon melee emerged on local news stations over the weekend, showing the fatal beating of Derrion Albert, a sophomore honor roll student at Christian Fenger Academy High School. His death was the latest addition to a rising toll: More than 30 students were killed last school year, and the city could exceed that number this year.
Prosecutors charged four teenagers Monday with fatally beating Albert, who was walking to a bus stop when he got caught up in the mob street fighting, authorities said.
The violence stemmed from a shooting early Thursday morning involving two groups of students from different neighborhoods, said Tandra Simonton, a spokeswoman for the Cook County prosecutor's office. When school ended, members of the groups began fighting near the Agape Community Center.
During the attack, captured in part on a bystander's cell phone video, Albert is struck on the head by one of several young men wielding wooden planks. After he falls to the ground and appears to try to get up, he is struck again and then kicked. Simonton said Albert was a bystander and not part of either group.
Prosecutors charged Silvonus Shannon, 19, Eugene Riley, 18, Eric Carson, 16, and Eugene Bailey, 18, with first-degree murder, Simonton said.
Shannon, Riley and Carson were ordered held without bond Monday. The Cook County Public Defender's Office, which represented the three teenagers in court, had no immediate comment. Bailey was due in bond court Tuesday, Simonton said.
Chicago police said they were looking for at least three more suspects, but would not discuss a possible motive for the attack.
Simonton said Albert was knocked unconscious when Carson struck him in the head with a board and a second person punched him in the face. Albert regained consciousness and was trying to get up when he was attacked a second time by five people, struck in the head with a board by Riley and stomped in the head by Shannon, Simonton said.
Desiyan Bacon, Bailey's aunt, said her nephew didn't have anything to do with the beating and was a friend of the victim.
"They need to stop the crime, but when they do it, they need to get the right person," Bacon said.
Fenger students said Albert's death intensified tensions at the school, with arguments about him breaking out in hallways all day Monday. Several blocks away, a memorial erected on the spot where he was beaten was burned down. Police also increased patrols before and after school and in the neighborhood.
"They're still trying to retaliate," said sophomore Toni Gardner, 15. She did not elaborate.
For Chicago, a sharp rise in violent student deaths during the past three school years -- most from shootings off school property -- have been a tragedy and an embarrassment.
Before 2006, an average of 10-15 students were fatally shot each year. That climbed to 24 fatal shootings in the 2006-07 school year, 23 deaths and 211 shootings in the 2007-08 school year and 34 deaths and 290 shootings last school year.
At a Monday vigil at the school, some community members said the solution lies with parents.
"It is our problem. We have to take control of our children," said Dawn Allen, who attended the vigil where a group of residents tried to force their way into the school before being turned back by police.
This month, the city announced a $30 million project that targets 1,200 high school pupils identified as most at risk to become victims of gun violence, giving them full-time mentors and part-time jobs to keep them off the streets. Some money also will pay for more security guards and to provide safe passage for students forced to travel through areas with active street gangs.
Albert's family attended a news conference Monday with school district leaders and police, but did not speak. They wore T-shirts with a picture of him in a cap and gown, with the words, "Gone too soon, too young."
But Annette Holt, mother of Blair Holt, a Chicago Public Schools student who was shot on a city bus two years ago, said Albert represented "another promising future, just snuffed out because of violence."
"Someone said he (Derrion) was in the wrong place at the wrong time," she said. "No, he wasn't. He was in the right place. He was coming from school."