Those threats were treated differently. December's resulted in the university closing for a day. The latest threat, reported to police just a week before the campus attack, resulted in no public warning to students.
On a Saturday night last December, in a women's bathroom on the sixth floor of Grant Tower at NIU, a student found something written on a toilet stall:
"What time? The VA Tech shooters messed up w/ having only one shooter," it said.
And then in different writing:
"Things will change most hastily
Tell those (N-WORDS) to go home."
Followed by shorthand for December 10, Holmes Student Center.
Northern students were outraged by the racial threat that invoked last spring's massacre at Virginia Tech, where 31 people were shot to death. The university closed down December 10, when the attack was to take place, but nothing happened.
"We don't know who did it, but we are more interested now than ever because we have had an incident and want to know who was responsible," said NIU Police Chief Donald Grady.
Then on Thursday February 7, in a different building, in a women's bathroom, a student found another threat handwritten in a toilet stall.
"It caught my eye because of how it was written. It wasn't very big but it was just very ? boom - line one, line two, line three, then the question mark and the date really caught my eye," said Beth Grotto, NIU senior.
The 21-year-old sociology student says she was concerned because of what happened in December, and she reported it to police. An officer took her information. She said the message looked freshly written.
"He just sounded like it was all routine, like he said what he had to say, he didn't sound very concerned about it," said Grotto.
"That threat was much more benign than the threat we had in December. Even on its face," said Chief Grady.
"I should have told somebody else, not just the police. I should have told the teacher, the administrator, somebody," said Grotto.
Chief Grady determined that what she found was not a credible threat and there was no public warning issued.
"It had none of the same earmarks that the threat in December had," he said.
The February threat was found in Dusable Hall, right behind Cole Hall, where the fatal attack occurred exactly one week later.
"It doesn't matter if it was related or not, it was a threat and especially after what happened in December, we as students had the right to know," said Grotto.
"We can create panic and hysteria by giving out warnings on every threat. What we don't want to have happen is to have emotions replace reason," said Chief Grady.
In an exclusive interview, Chief Grady says the FBI crime lab is comparing all the handwriting to that of the shooter in last week's lecture hall slaughter but that he doesn't believe there's a connection.
There is an unusual similarity. In the December threat, several letters are underlined that spell out the word: "watch," as in "watch out" or "watch me." In the February 7 threat, letters are underlined to spell the word "fear."
Because police say they don't know who wrote either threat, Grotto and her father, an NIU law school alum, say they are even more concerned that whoever wrote them is still out there.
"We may have several people writing these threats on the wall because the handwriting in these things may have come from different people. So each threat may have been written by multiple people," said Chief Grady.
Chief Grady says he doesn't want to minimize any students' fear or discourage reporting any threat. He would not disclose what police look for in threats to determine whether they are bona fide.