Updated 05/06/13 – 10:33 a.m.

LEMONT, Ill. (CBS) — Police officers and dogs searched two suburban schools after someone found a bomb threat scrawled on the wall of one of the buildings, but a search turned up “absolutely nothing.”

CBS 2’s Susanna Song reports officers and K-9 units were at Oakwood Elementary School and River Valley School in southwest suburban Lemont, after someone wrote a bomb threat on the wall in chalk at Oakwood. The two schools share the same campus in Lemont.

A passerby saw the threat on Sunday, and called police.

In a letter to parents, principals of both schools wrote, in part, “We received information from the Lemont Police Department that a bomb threat message had been written on an Oakwood school exterior wall. The threat indicated that Oakwood School will be bombed on Tuesday, May 7th.”

Before school started Monday morning, four K-9 units from the Cook County Sheriff’s Bomb Squad swept the two buildings, inside and out. Even before the search, though, police said there was “no credible threat.”

“As a parent, and as a police chief, there’s no way that we could afford to not take seriously a threat, no matter at what level, and that’s exactly what we did today?” Lemont Police Chief Kevin Shaughnessy said.

He said police found “absolutely nothing” in their search.

Police also planned to return to the schools Tuesday before class.

District 113A Superintendent Dr. Susan Birkenmaier said, “It’ll be different, but there will be a police presence. Staff will be present, and we will do everything we can to make sure students are safe.”

The schools will keep their normal schedule Monday and Tuesday, but police officers plan to supervise the schools’ hallways, and could check bags brought inside.

Some parents said they sat down and talked to their kids about the threat.

“She’s a little scared. We talked to her this morning, actually, and she’s like, ‘What’s a threat?’ and we had to explain to her a little bit,” Carolin Frusher said about her conversation with her daughter. “You kind of think about, ‘Can this happen in my town? Hope it doesn’t, but yeah, I suppose it could happen to our town.’”

Joel Lefevers said, “We thought about not bringing them, but what are you going to do? It was a threat, and they have to go to school.”

According to the schools’ student handbook, whoever is caught for writing the threat faces suspension or expulsion from school.

Shaughnessy said the culprit’s parents also could have to pay for the costs of the search. He estimated Monday’s activity alone cost thousands of dollars.

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