Police say witnesses saw a suspicious male in the Virginia Tech building where 30 people were killed and doors to the building were chained shut two days before the shootings.
Police held a news conference in Roanoke on Friday about the status of the investigation.
Virginia Tech police chief Wendell Flinchum says the suspicious man was seen at about 10 a.m. in Norris Hall on April 14. Student gunman Seung-Hui Cho carried out the killings in Norris Hall after killing two students in the West Ambler Johnston dormitory on April 16.
Cho had chained shut the Norris Hall exits before the shootings, then shot himself to death as police broke through the chains and stormed inside.
State Police said they don't know how long the doors to Norris Hall were chained shut that Saturday.
State police superintendent Col. Steven Flaherty said it would be speculation to say that the chained doors might have been a practice run on Cho's part.
Flaherty says they still don't have evidence linking Cho to his victims. He says investigators are still looking for Cho's cell phone and his computer hard drive.
CBS affiliate WDBJ in Roanoke also reported that the police disclosed today:
Cho apparently waited outside West Ambler-Johnston Hall until another student opened the door, allowing him to enter at 6:45 that morning. That is where Cho shot and killed Emily Hilscher and Ryan Clark. There is still no known reason why Cho selected Hilscher and Clark as targets.
Police found Cho's shirt and jeans hidden in a closet in his room; they had Clark's blood on them.
A bloody shoeprint outside Hilscher's room matches a bloody shoe found in Cho's dormitory room.
Cho had written "Ax Ishmael" in red ink on his left arm the day of the shootings.
There is no known connection between Cho and earlier bomb threats on campus, but he did leave a written bomb threat in Norris Hall the morning of April 16. An employee took the note off the door and handed it to a custodian. Police found it in a classroom that afternoon, after the rampage had ended.
Cho mailed a letter to the Virginia Tech English Department at 9:01 a.m. that day. Like the "Manifesto" he mailed to NBC News, it is described as rambling and incoherent and of little value to the investigation.