Four white students were arrested Friday, charged with inciting violence, false alarm, aggravated menacing, ethnic intimidation and inducing panic. Cleveland Mayor Michael White said authorities were questioning up to seven more students.
The mayor described a plot that was racially motivated and said the suspects were white and the school has a majority black enrollment.
Dan Shields, who represents a brother and sister who were questioned in the alleged threat, contends that White overreacted in canceling classes Friday.
"South High School is not Columbine," Shields said in reference to the nation's deadliest school shooting last April.
"There's no weapons at school, no violent acts. We understand there may have been some talk from one child regarding some actions against other students, but that's it."
Shields also noted that no charges have been filed against his clients, a 14-year-old boy and his 15-year-old sister.
White didn't disclose the names of those arrested but a local newspaper, The Plain Dealer, citing juvenile court records, identified them Friday as Adam Gruber, 14, and 15-year-olds John Borowski, Benjamin Balducci and Andy Napier.
The newspaper said Napier was the ringleader and that his parents have admitted him to MetroHealth Medical Center for a psychiatric evaluation. The other three are in juvenile detention.
Police began their watch over the school on Friday, closed for what would have been Homecoming weekend, reports CBS News Correspondent Cynthia Bowers.
Police confiscated two guns from a home Friday, but no firearms or explosives were found in the school. White wouldn't comment Friday on the report that the plan had been for a Columbine-style attack. And he wouldn't say whether authorities think the guns they found were related to the alleged plot.
At Columbine, Eric Harris, 18, and Dylan Klebold, 17, killed 13 people and wounded 23 others at the school on April 20 before killing themselves.
The South plan, which police say was to have been carried out Friday, was averted when a scared student came forward.
According to 15-year-old South student Sarah Jedd, the teens police are investigating "just started talking about going into the school and just start killing people. It would be random, anybody who got in the way."
Jedd was questioned by police because her name is on a document linked to the plot. With chilling detail, she described to CBS News where each of the gunmen -- her friends Adam, Andy and John -- planned to be when they began shooting.
Jedd said the plan called for "Adam in the basement, wherever he could be, John was gonna be in the hallways, Andy was going to take care of the office and tuff like that." She said they would then "just run around and open fire."
She also told of plans for a suicide plot: "They said they were gonna stand in a circle type thing and just start shooting off. And whoever survived they said was gonna bask in the glory, and that means rotting in jail for the rest of their life, and that's supposed to be glory."
Jedd said she didn't come forward at first because her friends had threatened her, saying, "You are either with us or against us, and if you are against us, you are going to die."
The broken-hearted grandmother of one of the accused boys admits she's been worried, even calling child services begging for help. "I've tried to help Adam for a long time," Joyce Gruber tearfully explained. "I could see that he was confused and hurting someway or another, but nobody listened to me."
Just how troubled one young suspect may be is evident in a South High yearbook, where he describes himself as "your friendly neighborhood psycho," and cautions, "I know where you live. Be afraid."
School Superintendent Barbara Byrd-Bennett said classes would resume at South on Monday with heightened security. She said police officers would be in the school and scan students with hand-held metal detectors. The school has 1,500 students.
Those assurances did not calm the fears of Richard Talbott, whose daughter, Takila, is a junior at South. He said he probably would not let her return to school on Monday.
"I don't think they can say anything right now to make me feel safe," he said.