Ten days into their investigation, authorities cannot explain exactly what prompted Seung-Hui Cho to shoot 32 members of the Virginia Tech community before turning the gun on himself.
They can't show any evidence of a relationship between Cho, a 23-year-old senior, and Emily Hilscher, believed to be Cho's first victim inside West Ambler Johnston Hall.
"At this particular point in time, we don't have a motive," Col. Steven Flaherty, head of the Virginia State Police, said at a press conference Wednesday. "We talk about possible motives and theories and whatnot, but we don't have any evidence to support these."
Virginia Tech Police Chief Wendell Flinchum said that authorities have followed up on "hundreds" of leads since the shootings took place Monday, April 16. They've collected some 500 evidence samples and interviewed more than a hundred people.
Authorities also have combed through computer records of Hilscher's campus e-mail account, in addition to Cho's complete computer and phone records, in hopes of finding something to connect the two and explain precisely what triggered the rampage.
"There's no link in our evidence at this particular point in time that links Cho to his first victims," Flaherty said.
New details about the bloody morning's timeline, however, were revealed. Witnesses told police they spotted Cho "just standing there" -- outside the dorm where the first shooting took place -- shortly before 7 a.m.
Ryan Clark, a dormitory resident adviser, responded to a commotion in a fourth-floor room, and then at 7:20 a.m., a rescue call came in about what sounded like someone falling off a loft or out of bed.
Police arrived to find Hilscher and Clark dead and immediately opened a murder investigation, identifying an initial off-campus suspect when a call came in at 9:42 a.m. about a second shooting inside Norris Hall, a Virginia Tech academic building.
In all, Cho's shooting rampage inside the building lasted nine minutes. It took police three minutes to respond to the scene and another five minutes to break through chains that Cho had used to lock the building's three public entrances.
Police heard a final gunshot -- presumably Cho's suicide shot -- before entering one of the four classrooms he targeted and discovering his corpse among some of his 30 Norris Hall victims. Cho fired more than 170 rounds, a shot every three seconds, inside the building where he had once attended class, Flinchum said.
Two handguns were retrieved near Cho's body: a .22 caliber model that was purchased in February from a Wisconsin dealer and a 9 mm model that Cho bought at a Roanoke gun shop. To lock the building's doors, Cho also bought chains from local shops that police would not identify.
Investigators said Wednesday there was no evidence linking the bomb threats that were made against Norris Hall in the weeks before the massacre to Cho 's rampage.
Besides Cho's trip to the Blacksburg Post Office, where he mailed a packet of photos, videos and writings to NBC, authorities know little about what happened in between the two shootings, except that at one point Cho returned to his own dormitory, Harper Hall.
For the most part authorities would not comment on Cho's mental state, but Flaherty did acknowledge a psychological profile that's impossible to ignore.
"He appears, in my humble opinion, to certainly be a troubled individual," Flaherty said.