The University of North Carolina at Charlotte lifted a campus lockdown on Wednesday morning, a day after a gunman killed two people and wounded four on the school's last day of classes for the semester. Police in Charlotte charged UNC Charlotte student Trystan Andrew Terrell, 22, with two counts of murder and four of attempted murder. Three of the four people he wounded were in a critical condition on Wednesday. They offered no hints as to the suspect's motive and did not identify the victims. Students on the campus spent a harrowing night as police searched door-to-door for any other suspects, not giving people the all-clear to move around till almost dawn. "This is the saddest day in UNC Charlotte's history," the school's chancellor, Phil Dubois, said in a letter to the community posted on the school's website. "Families of the deceased victims are being notified and university staff are with those who are injured." The shooting started at about 5:40 p.m. on Tuesday police said, in a classroom. Tristan Field, a student who witnessed the shooting, told CBS News as many as 50 students tried to escape through two doors. "A chair fell in front of the door, so people were tripping over that, like, trying to climb over it," he said. "Some people fell down. It was like water through a funnel but wasn't fast enough." The gunman was disarmed by two or three campus police officers who entered the building after responding to an emergency call, campus Police Chief Jeff Baker said. A vigil was planned at the school for Wednesday, CBS news reported. Sandy D'Elousa, a spokeswoman for the Charlotte-Mecklenburg Police Department, which is leading the investigation, said the gunman was believed to have acted alone. North Carolina Governor Roy Cooper called the incident a tragic day for the university and the state just a few days before graduation. "But I know the people in this community, and they will be here for each other," he said at a news conference. According to its website, the University of North Carolina at Charlotte has more than 26,500 students. The deadliest mass shooting on a higher education campus in the United States took place at Virginia Tech University in Blacksburg, Virginia, in April 2007, when a student killed 32 people and then himself. — Reuters