Thursday was Purdue's first day back in class since the tragedy in the Electrical Engineering building.
While shooting suspect Cody Cousins made his first appearance before a judge, the university was planning a review of its security response.
"It's common to have people who will complain afterwards, it's common to reflect afterwards to make sure that we did everything right. Even if we did everything well, like we did in this case," said Purdue homeland security expert Dr. Eric Dietz.
Purdue University President Mitch Daniels said Wednesday night he wants to look into complaints that some staff members did not follow procedures.
"There were hundreds on hundreds of classes going on, it's very clear virtually all of those were handled well, but in some cases it wasn't," said Daniels.
Some students on social media said professors in some cases continued to teach even after text alert messages went out about a shooting. They say the lights in classrooms stayed on and doors were not locked.
But Dietz, who helped design Purdue's emergency response plan, said "shelter in place" means that - stay put.
"Doesn't necessarily mean you have to turn out the lights or barricade you in a room. Many of our doors do not have locks," he said.
He says he might even have continued teaching under some circumstances.
Meanwhile, some of Dietz's graduate students have been working on the issue of active shooters getting into schools. Two of those grad students stand over a computer in the building next to the crime scene, showing Eyewitness News a computer model of a fictitious active shooter inside a fictitious school.
"What he's probably going to do is enter this classroom here," said graduate student Adam Kirby, pointing to a representation of a classroom on his graphic.
In this scenario, the fictitious school has a trained, armed school resource officer and local police are beginning to arrive at the school.
But "it took him 8.2 minutes to engage the shooter and four people were shot," said Kirby.
Then they ran another scenario that assumed local police get into the building, the armed resource officer finds the suspect and some school staff are licensed to carry a concealed firearm in the school.
That scenario gives researchers "an aggregate reduction of nearly 60 percent in casualties and nearly 50 percent response time," said researcher Chuck Anklam.
The researchers caution the data does not reflect every real-world active shooter scenario. But school staff carrying weapons is a hot button and controversial issue.
"We're going to have to figure out what works in a policy environments and the political environment we are in," Dietz said.