Speaking at a press conference on the college's campus, Virginia state police superintendent Steve Flaherty said: "We are trying to determine what happened and as much as possible, why, why this terrible tragedy occurred.
"A lot of folks saw images that were very disturbing.
"This is a kind of image that people in my line of work have to see, and I'm worried that people who are not used to seeing them had to see them."
On the footage, NBC's head of news Steve Capus admitted that there was "no way to look at [it] without being profoundly upset, and it is incredibly disturbing".
"I'm not sure we'll ever fully understand why this happened, but I do think this is as close as we'll come to having a glimpse inside the mind of a killer," he added.
Today's dramatic developments follow the police revelation that the English undergraduate was temporarily admitted to a mental health unit in late 2005 after two female students made complaints that he had stalked them.
In one video clip, 23-year-old Cho rants to the camera: "You had a hundred billion chances and ways to have avoided today.
"But you decided to spill my blood. You forced me into a corner and gave me only one option. The decision was yours.
"Now you have blood on your hands that will never wash off," he adds in a chilling final message.
As a worrying picture of Cho begins to emerge, questions have begun to be raised about why the authorities failed to heed warning signs in regard to the behaviour of the South Korean national, who was also referred for counselling by his college teachers after penning a series of disturbing writings.
In the latest twist, NBC revealed that the package they received from Cho contained a rambling written statement, 23 video clips and 43 photos, many of which showed him pointing handguns at the camera.
A postal stamp showed that the package had been sent from the post office in Blacksburg, Virginia, in between the two separate shooting incidents at the town's Virginia Tech college on Monday morning.
Cho is understood to have murdered 30 people in classrooms on the campus - where he himself was a student - before killing himself and police are also continuing to assess evidence to link him to a separate shooting two hours earlier, in which two students were killed in one of the college's dormitories.
In the 1,800-word written rant contained in the package Cho makes a disturbing mention of "martyrs like Eric and Dylan," in an apparent reference to the Columbine shooters Eric Harris and Dylan Klebold, who shot dead 12 students and a teacher at the school in Colorado in 1999.
NBC said that it received the chilling delivery on Wednesday morning, two days after the shootings at Virginia Tech, with the receipt of the package thought to have been delayed by the use of a wrong postal zip code.
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