A third teenager arrested in what police call a Columbine-like plot to attack East High School helped make jelled gasoline and tested it last winter, a prosecutor said Monday.

Brown County District Attorney John Zakowski told Court Commissioner Larry Gazeley that the three friends started planning to assault the school with guns and explosives two to three years ago, based on the three teens' statements.

Police arrested William Cornell, 17, and Shawn Sturtz, 17, on Thursday and Bradley Netwal, 18, on Friday for conspiracy to commit first-degree homicide and arson. Another student alerted an associate principal to the alleged plot.

Formal charges are expected later in the week.

Netwal was in an orange jail suit and appeared by video conference from the Brown County Jail. He kept quiet through the hearing, which was for the prosecutor to prove there was enough evidence to hold the teen.

Gazeley ordered Netwal jailed on $500,000 cash bail, and set his initial court appearance for Friday.

Bail for the other two was set at $500,000 last week. Their first court appearance was scheduled for Thursday.

Zakowski said that at one point, Netwal suggested that the assault be a drive-by shooting because it would be easier to get away.

Zakowski said that they know of no other conspirators in the plot so far.

Netwal's attorney, Christopher Froelich, said the teenager was not involved in the plot.

"My client has no control over what other people do or think," he said.

No guns or evidence of any plot was found in Netwal's home, Froelich said.

But Zakowski said that like Cornell and Sturtz, Netwal wanted some revenge for problems he was having at the school. Netwal knew Cornell for three years and they started talking about a Columbine-like plot in fall 2004, Zakowski said.

"He did admit that he and Bill made (jelled gasoline) and he knew Billy was purchasing weapons," the prosecutor said.

Zakowski said Netwal knew Cornell had recently sawed off a shotgun and the two went target shooting last week.

"Billy told him he would have to do something soon because his dad would soon find out (about the gun)," Zakowski said.

Police Capt. Lisa Sterr said the two 17-year-olds had long been fascinated by the April 1999 Columbine massacre in Littleton, Colo., in which two armed students killed 12 classmates and a teacher before killing themselves.

Police found nine rifles and shotguns, a handgun, about 20 "crudely made" explosive devices, camouflage clothing, gas masks, two-way radios and hundreds of rounds of ammunition at Cornell's house, Sterr said.

At Sturtz's home, police said they found knives and ammunition.