CHICAGO (CBS) – They watched in shocked silence. Some even cried. On Tuesday, jurors in the trial of a teenage boy were shown the videotaped beating that ended 16-year-old Derrion Albert’s life. CBS 2’s Vince Gerasole reports.

The gruesome violence surrounding Derrion’s death is unthinkable. He was walking home from Fenger High School on Sept. 24, 2009, when he was attacked in front of the Agape Community Center, 342 W. 111th St.

What prosecutors called the actions of a mob were played on video over and over with scenes of young men beating each other with sticks as large as railroad ties.

In court on Tuesday, Derrion’s family sobbed as jurors watched a tape of him being beaten. The sight of the wounded teen brought a few jurors to tears as several of his family members had to leave the courtroom.

Through it all, the teenage defendant, a tall boy dressed in a grey vest, sat still with his eyes to the ground.

Derrion was caught in a fight between two groups of Fenger students — one from the Altgeld Gardens neighborhood and another who live in an area known as the “Ville,” prosecutors said. He was bludgeoned in the head with the railroad tie, stomped, punched and pushed to the ground during the melee, prosecutors said.

LISTEN: Newsradio 780’s Mary Frances Bragiel Reports

The fight was captured on a cell phone video, which was seen around the world and drew unflattering attention to the city.

The most emotional testimony came from a social worker who witnessed the attack from the Agape Community Center. Prosecutors asked T-Wanda Piper to narrate the video.

She said, “I saw a young man hit a boy over the head with a board.”

She then broke down crying. The victim was Derrion Albert.

Of the defendant, Piper said, “I saw him hit him in the face with his fist. Derrion fell to the ground and other young men started to surround him and kick him.”

Piper eventually ran to an injured Derrion.

“I went over to him, wrapped my arms around him and picked him up,” she said. “He gasped for breath as if trying to respond but he couldn’t.”

But defense attorney Richard Kloak drew different conclusions from the video. His client is seen handing a large board to someone else, but the defendant only hits Derrion in the face once.

“He had a minimal role,” Kloak said of his teenage client. “He didn’t hit anyone with a board or a stick. He got involved. That is wrong, but he is not guilty of first degree murder.”

If convicted, the boy could be locked up until he is 21.

Four others are charged as adults in the killing and are currently awaiting trial. They are Eugene Riley, 19, Lapoleon Colbert, 20, Silvonus Shannon, 20, and Eric Carson, 17.

Derrion Albert’s death prompted President Barack Obama to call for a national conversation on violence. The month after the incident, U.S. Atty. Gen. Eric Holder and U.S. Education Sec. Arne Duncan visited Chicago to discuss ways to combat youth violence.

Though many of Derrion’s family members were inside the courtroom, his mother chose to remain outside while the beating video was played.

Watch & Listen LIVE