ST. LOUIS • The middle-schoolers were looking for a random person to beat up on Oct. 21, hoping to prove their mettle to a group of teens at Roosevelt High School who called themselves "TKO" or "The Knock Out" clan, police say.

They found their victim in Matt Quain, kicking and punching him in the face, breaking his jaw and knocking him down on South Grand Boulevard before walking off.

The 13-year-old girl who relayed this to police became the key witness against seven juveniles, ages 12-14, all from Fanning Middle School. But at the last minute before trial this week, she failed to show up, and the case fell apart, as was first reported Wednesday on STLtoday.com.

The witness has refused to cooperate any further, forcing prosecutors to drop the second-degree assault charges against the six boys and one girl, court spokesman Matt Murphy confirmed. He would not provide any more detail about the witness, given that it is a juvenile court matter.

Mayor Francis Slay and his bodyguard, a city police sergeant, happened by as the teens walked off after the attack. But they didn't get a good look, nor did Quain, who was knocked unconscious.

"It's disturbing," said Quain, 52, of St. Louis, who is still recovering from the attack. "They got away with it. Our case just didn't hold water."

The adjudication hearing Monday in which the girl failed to show was the equivalent of a trial in adult court. Afterward, the teen defendants, who had been held in detention until then, were free to go.

Quain said that during the hearing, the teens "were looking me over like I was a piece of meat." Afterward, he watched as they celebrated in the hallway outside the courtroom. "They were cheering and high-fiving," Quain said. "It was like a big game to them."

The chief trial attorney who handled the case, Margaret Gangle, could not be reached for comment Wednesday. A defense attorney for one accused teen declined comment.

The "knockout game" involves random, unprovoked attacks on unsuspecting victims, usually by teens who have no discernible motive other than to beat someone up. The Oct. 21 attack was one of seven cases last year that police identified as being motivated by the "game."

After the assault on Quain, police zeroed in on Fanning and Roosevelt schools. It prompted a new outreach effort in an attempt to warn students against participating in the violence, and urge them to help police stem it. Police said the collapse of Quain's case underlines the importance of witness cooperation.

"It is always frustrating when we see cases dropped after officers have worked hard to make arrests," said Katie O'Sullivan, a police spokeswoman. "We continue to need assistance from witnesses who will come forward when they see criminal activity in our neighborhoods. We also need those witnesses to cooperate throughout the judicial process in order to assist prosecutors with their cases."

Slay, who said he was "very disappointed and angry" about the case being dismissed, echoed O'Sullivan's sentiments.

"I feel for the young girl," Slay said. "I mean, clearly, she was intimidated (into) not testifying. We need to support witnesses like we support victims."

Slay added: "The police know who these thugs are. They know where they go to school, and they know where they live. Neither I nor the police are going to forget about this."

Emily Luten, whose boyfriend was the victim of a similar assault, expressed frustration about the outcome of Quain's case.

"I understand the system — I would never want to be in a situation where they could try me without a witness — but there needs to be a way to make sure it's safe on the streets," she said.

No one has been charged in the assault on Luten's boyfriend.

Quain and a neighbor were walking home from a Schnucks store on South Grand Boulevard about 11:40 p.m. They were a few blocks from their apartment building when a group of teens surprised them near the Carpenter branch public library.

According to a newly obtained police report, the 13-year-old witness told detectives the attackers were students at Fanning Middle School hoping to "earn their stripes" among students at Roosevelt High School who identified themselves as a group called "TKO" or "The Knock Out" that targets and attacks random people as part of a game.

She told police at least two boys punched Quain and four more boys and a girl joined in the attack by kicking and punching him in his head, face and body, according to a police report.

Using the witness' statements and comments about the knockout game posted to one of the suspects' Facebook pages, police took custody of five boys and a girl who attended Fanning Middle School on Oct. 28, according to the report. On Nov. 2, police arrested another juvenile at Stevens Middle School.

Quain has worked as a dishwasher for more than seven years at Joanie's Pizza in Soulard. He returned to the shop on a part-time basis two weeks ago and hopes to return full time as soon as he fully recovers.

Quain said he worries the violence isn't going to stop: "I don't doubt that they're going to do it again. ... The choices those kids make will come back to haunt them someday, I hope."