Last week authorities in South Bend, Ind., accused a 16-year-old of planning a Columbine-style attack on his high school in Mishawaka.

Police said they obtained e-mails that pointed to the teen seeking help to obtain a TEC-DC9 9mm pistol. Prosecutors quoted the teen as saying it would be "awesome" to carry out mass murder in two states on Sept. 11 using the same weapon as the Columbine killers.

Just a week earlier, an 18-year-old in South Carolina was arrested after his parents turned him in for allegedly buying ammonium nitrate, the same chemical used in the Oklahoma City bombing.

According to police, the troubled youth alluded to the Columbine massacre in some of his writings.

The two incidents were hundreds of miles apart, but they were bound by a common thread: Columbine.

"Columbine was the Pearl Harbor of education and school safety," said Kenneth Trump of National School Safety and Security Services. "Unfortunately we are still feeling the shock waves."

On April 20, 1999, Eric Harris and Dylan Klebold killed 12 classmates and a teacher in a five-hour rampage of gunfire and bombs at Columbine High School in Littleton, Colo.

When the horror was over, the two students committed suicide.

Nearly a decade later, their dark legacy still haunts the nation. There is a growing list of young killers or would-be killers -- some barely old enough to remember Columbine -- who appear fascinated by the young murderers.

The connection is quite clear, with these troubled young people specifically writing or talking about their admiration for the Columbine killers or mimicking their actions by wearing black attire and their desire for fame.

A closer look by ABC News reveals a disturbing picture.

December 2007: A Nebraska shooter, clad in black, wrote he would be famous before a killing spree at a mall.

December 2007: A Colorado shooter killed four people in two separate incidents. He specifically mentioned the Columbine killers in angry writings.

November 2007: Finnish high school student Pekka-Eric Auvinen shot and killed six students, a nurse and the principal, then committed suicide. He left behind a manifesto saying the shootings were part of his belief in natural selection. He also belonged to a Web site dedicated to the Columbine killers.

October 2007: A 14-year-old Philadelphia student and user of the same Columbine killer Web site was arrested on suspicion of planning a Columbine-style assault. He is suspected of having communicated with the Finnish killer via the Columbine shrine Web site.

February 2007: An 18-year-old shot and killed five at a Utah mall before being shot to death by police. Neighbors of the teen said he often dressed in black, like the killers from Columbine.

April 2007: The Virginia Tech shooter had written of his admiration for the Columbine killers before the worst college campus mass murder in U.S. history. Thirty-three people died, including the shooter.

Trump attributes this disturbing legacy primarily to two issues:

The Columbine massacre has become "so engrained in our culture -- to the point it has become part of the vernacular," he said. To do a "Columbine" is now the equivalent of "going postal." Columbine symbolizes a planned school assault in the same way "going postal" is associated with workplace violence.

Trump said there are many "kids going to school with serious undiagnosed mental health issues."

Those troubled youth are aware of Columbine's infamy and can find information about the assault through the Internet.

After Columbine, many school systems are much more sensitive and quick to respond to such threats, but the threats are not going away.