Virginia state police said they have yet to find a link between the gunman in the shootings at Virginia Tech on April 16 and his 32 victims.

"There is no link in our evidence that links [Sueng-Hui] Cho to either of his first victims," Col. Steve Flaherty said in a Wednesday news conference.

"We're following a number of leads."

Flaherty said that witnesses saw Cho outside of West Ambler Johnston Hall -- where he shot Emily Hilsher and Ryan Clark -- before 7 a.m. the day of the shooting. He added that Cho may have returned to his residence hall between the first shooting and the second one at Norris Hall.

Police have combed through the phone records and computer files of Cho, but have found no evidence as to what triggered the 23-year-old's massacre that ended when he turned one of his guns on himself.

Virginia Tech Police Chief Wendell Flinchum confirmed that Cho chained shut three doors at Norris Hall that delayed the ability for police to get in the building after they arrived at the scene, and students to leave.

Cho killed 30 people in Norris Hall before shooting himself. Flaherty said 25 people were injured at that site -- some were shot, others from jumping out windows in an effort to flee Cho.

Flaherty said the video Cho made and sent to NBC News along with pictures and a manifesto was made before the shooting.

"We know it was done before the 16th," he said. Flaherty said he wasn't prepared to share when or where the video was made.