Norris Hall is seen as police secure the area on the Virginia Tech campus in Blacksburg, Virginia, after the building was evacuated on April 18, 2007. Thursday is the eighth anniversary of the mass shooting. Reuters

Virginia Tech senior Seung-Hui Cho sneaked into the West Ambler Johnston residence hall and shot two students on April 16, 2007, at 7:15 a.m. He left, stopped by the post office and later headed to Norris Hall. About two hours later, Cho chained the doors shut and began entering classrooms, killing professors and students before fatally shooting himself in the head. Including Cho, 33 people died that day. More than 20 were wounded.

The Virginia Tech massacre, known as the deadliest school shooting in U.S. history, motivated colleges and universities to quickly improve the security on their campuses. Administrators have concentrated on updating communications systems, while politicians have changed gun control laws to limit access to firearms by the mentally ill. But eight years later, as state officials debate concealed carry laws, there's still room for improvement, as recent shootings in California and North Carolina show.

"The 2007 mass casualty incident at Virginia Tech was a turning point for a lot of campuses -- or a rallying point," said Gene Deisinger, managing partner at SIGMA Threat Management Associates in Blacksburg, Virginia.

After the shooting, investigators discovered that a judge had ruled Cho was mentally ill in 2005, but his records were never entered into a mental health database that would have prevented him from buying guns. Virginia Tech was criticized for not notifying the campus soon enough after police responded to Cho's first killings in the dorm. The university sent out its first warning at 9:26 a.m., only 14 minutes before the gunman started shooting in Norris Hall.

The shooting was tragic, and it was a wakeup call for colleges, said S. Daniel Carter, director of the Centreville, Virginia, 32 National Campus Safety Initiative, which educates people about school threats. Higher education institutions that had outdated or inefficient emergency plans realized they needed to update or fix them. "That one incident sort of crystallized campus safety in people's minds as a very, very serious issue," Carter added.

In some cases, action came in the form of immediate legislation. Former Virginia Gov. Tim Kaine that summer signed an executive order mandating that the names of people who received involuntary treatment for mental illness be turned over to the FBI's National Instant Criminal Background Check System. Individuals whose names turned up there would not be allowed to legally purchase a gun until the courts declared them stable, according to the Washington Post. Former President George W. Bush approved a law in January 2008 strengthening the system and giving states money to keep it updated. That same year, Congress added an emergency notification requirement to the Jeanne Cleary Act that forced colleges to put out timely warnings in crisis situations. The law requires colleges that receive federal aid to provide records of campus crimes.

In the meantime, schools expanded their communication strategies. In 2007, many colleges were looking into multiplatform alert systems that could notify students and faculty when something went wrong on campus. The Virginia Tech shooting pushed administrators to roll them out faster.

The University of Iowa, where former student Gang Lu killed four faculty members and a student in 1991, launched its Hawk Alert system about five months after the Virginia Tech massacre. The school later put up towers on campus that could broadcast audio and play sirens, the Daily Iowan reported.

Virginia Tech now has the capability to disseminate emergency information via phone call, email, text message, website, Twitter, hotline and loudspeaker, said Michael J. Mulhare, director of emergency management. His office has developed templates for each platform so they can publish alerts as soon as possible. They've learned to keep the messages under 140 characters. "We try to do three things: let the community know what happened, where it happened and what action we want the community to take," Mulhare said.

Virginia Tech also upped it efforts to train faculty and students on what to do in a dangerous situation. This can be difficult because of the frequent turnover in the school's population. Mulhare said the university focuses on teaching people how to quickly access resources. Virginia Tech has a centralized website with emergency plans that also appear in the app LiveSafe. These tools keep people in the know and phone lines open. Previously, when the school sent out a warning about an incident, people would clog dispatch asking what to do, Mulhare said. Now all they have to do is swipe.

The Virginia Tech shooting led several schools to create threat assessment offices that identify dangerous cases and try to intervene before there's an incident. Northern Illinois University, where Steven Kazmierczak fatally shot five people and himself in February 2008, put together two assessment teams. One is for students; the other is for employees, according to a 322-page report the school commissioned after the tragedy.

Deisinger, a former threat assessment manager with the Virginia Tech Police Department, said these teams help schools be proactive rather than reactive. About 80 percent of U.S. colleges have created threat assessment teams since 2007, according to USA Today. Virginia and Illinois require them by law. "It's getting more built into our culture," he added.

Other education leaders are trying different methods to address school shootings. Laws and university policies in 41 states ban students and faculty from carrying concealed firearms on campus, the New York Times reported. Seven states allow it, and that number could soon grow -- a further 15 have introduced bills this year to legalize campus carry. Florida, Indiana, Nevada, Ohio and Texas are among the states weighing looser restrictions. One of the arguments for campus carry is that students and faculty could protect themselves in active shooter situations.

Interest in college security fluctuates, Deisinger said, because Americans are driven by big events that catch their attention. Virginia Tech sparked a lot of change, he said, but campus safety requires constant discussion.

There's a great deal more of work to be done -- the Huffington Post counted at least 27 college campus shootings in 2013, and gun control group Everytown listed more than 30 in 2014. "In the best situations, with the best people with the best training, bad things will still happen," Deisinger said. "We can't eliminate risk. ... We can simply make it harder for bad acts to occur."