First, Virginia Tech it is quite large (2600 acres), several miles across each way, hundreds of buildings, and at least 30,000 people on campus during the time of this incident. Closing campus and evacuating 30,000 people OFF of campus can't be done with the push of a button and especially with this situation it would have created a general panic within the community that would have caused even more problems then solutions. Imagine the traffic jams with several THOUSANDS of cars leaving all at once onto a relatively limited amounts of exits from the university. 

Second, if every incident resulted in a full swat response, not much of anything else would get done.  Investigators assessed the situation.  It appeared to be a one off lovers revenge incident.  Not that this is not a horrific tragedy in itself.  All our hearts go out to the victims.

Third, we should stop thinking about CSI and that everything in law enforcement happens instantaneously now. Interviewing witnesses, processing crime scenes, gathering evidence take HOURS and sometimes DAYS depending on the crime.  If the first murder happened within two hours, the investigators would have been lucky to get a suspect description and find a few witnesses. However, they had already developed a suspect and information, from  a witness, to believe the suspect  had already left campus and was believed to be fleeing the state . Never the less, everyone expects a decision to shut down the university which is basically a small town of 30,000 people immediately, especially when the AVAILABLE INFORMATION is that the police believe the suspect left and was gone BASED ON witness information which is ALL they have to go on at that point in time. Just think about the circumstances and vastness of this tradgedy and stop blaming people already before we know all of the information available. The honest truth  is if someone has already made up their mind that they want to kill someone and have no problem with dying themselves, there is little anyone including any law enforcement official can do to stop that person with that much determination. Unfortunately, the person that committed these acts was one of those persons.

Additionally, any one of the responding officers would have done everything to save as many people as they could because that is what  they do. Take a step back and really look at what happened and see that there is something very seriously wrong with a nation that  allows anyone to  buy guns and take them to school.