Two colleges in the Chicago area reopened and followed their regular class schedules after graffiti threats warning about a doomsday did not materialize. One university remained closed, as administrators are still analyzing whether the threats should be considered dangerous.

After discovering a threatening graffiti message in a bathroom of St. Xavier University, administrators told students to keep off campus. The message, reading "Be prepared to die on 4/14," caused not only the Catholic liberal arts college to close, but also four other elementary and high schools situated in the area.

A similar message was also found in a bathroom at Malcolm X College, which was also closed on Monday. St. Xavier and Malcolm X are situated about 15 miles apart, but it was not confirmed that the threats in the two institutions were related, according to Chicago police spokeswoman Monique Bond.

Michigan's Oakland University was also shut down on April 14, but it reopened on Tuesday, as well as Malcolm X College.

"We feel it is safe to return to normal operations Tuesday," Oakland University Chief of Police Sam Lucido said in a statement.

The threats should not be so surprising, school safety experts say, as they come around the anniversary of the Columbine and Virginia Tech massacres.

On April 16, 2007, at Virginia Tech, a gunman killed 32 people and injured more than 20 before committing suicide.

On April 20, 1999, two students at the Columbine High School in Colorado shot to death 12 students and a teacher, also wounding 23 others. Like the killer in the Virginia Tech case, the boys have both committed suicide after their actions.

District superintendent Craig Fiegel said schools should only be closed as a last resort following threats such as the recent ones. He worries that school closures could encourage people to cause chaos just for fun.