The eerie message arrived Wednesday via express mail in a package of photographs, videos and writings sent to NBC News on Monday, the day of the shooting, network officials and police said Wednesday. Click here to watch video.

The 9:01 am postmark on the package indicated that 23-year-old Cho Seung-Huimay have paused between two shooting incidents on campus to mail a carefully prepared package of 23 video files, an 1,800 word manifesto and 29 photographs.

"You had a hundred billion chances and ways to have avoided today," Cho said in one of video files, accompanied by numerous still shots of him wielding pistols.

"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 addressed the package to NBC news head Steve Capus. The postmark shows he paid 14 dollars and the package was mailed from a post office in Blacksburg where Virginia Tech university is located.

NBC anchor Brian Williams described the contents as a "very long multimedia manifesto."

The English major appears to be wearing different clothes and filming himself in different locations in the various clips in which he describes his anger and hatred for the wealthy.

"I didn't have to do this. I could have left. I could have fled. But no, I will no longer run. It's not for me. For my children, for my brothers and sisters that you (expletive). I did it for them," Cho said on one of the videos.

"Do you know what it feels like to be torched alive? Do you know what it feels like to be humiliated? You had everything you wanted."

Capus described the written statement as "hard to follow, kind of rambling ... In one instance he makes a vague reference to the massacre and says 'This didn't have to happen.'

"He speaks about hatred," Capus said, adding it was "disturbing, very angry, profanity-laced."

In one of the still pictures in the package, Cho brandishes a pair of handguns, pointing them slightly outward as he stares down the camera with a fierce expression.

In another, Cho points a silver pistol directly at the camera.

In some shots he is wearing a black baseball cap backwards and the same short-sleeved khaki survival top and black vest that was described by student witnesses who survived the shooting.

Virginia police superintendent Steve Flaherty told a news conference the "correspondence included multiple photographs, video and writings," and said the material had been turned over to the Federal Bureau of Investigation.

"This may be a very new critical component of this investigation. We are in the process right now of attempting to analyze and evaluate its worth," he said.

The South Korean native's fatal rampage at Virginia Tech University on Monday marked the deadliest school shooting in US history.

NBC said on its website that it believed the material had been sent after a first shooting incident on Monday at the university but before the mass shooting in a second school building.

"Sometime after he killed two people in a dormitory but before he slaughtered 30 more in a classroom building Monday morning, Cho Seung-Hui sent NBC News a rambling communication and videos about his grievances," the network said.

The package was "time stamped in the two-hour window between Monday's shootings," NBC news said on its website.

Police however still not confirmed whether Cho was responsible for both shootings -- the first early in the morning in which two students were killed and the second in which 30 people were gunned down before Cho fatally shot himself.

Agence France-Presse