This frame-grab image is taken from a video aired by NBC News yesterday. Associated Press/NBC

Cho mailed the package, which contained an 1,800-word diatribe and multiple photos of him aiming handguns at the camera, at 9:01 Monday morning. That was nearly two hours after he had killed two students in a dormitory and minutes before he stormed a classroom building and killed 30 people before turning a gun on himself.

He sent his parcel to NBC in New York, which made copies of the material before turning it over to authorities.

In an often incoherent monotone laced with obscenities, Cho says, "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."

In one of the more than 40 still photographs, Cho poses with arms outstretched, his hands in black gloves, as he points two firearms — presumably the Walther P22 and the 9-millimeter Glock he used to gun down students and teachers. Dressed in a black shirt and khaki military-style vest and wearing a black cap turned backward, Cho stares ominously into the camera.

"When the time came, I did it," he says. "I had to."

Federal law-enforcement sources said Cho sent his manifesto, which was steeped in profanity and railed against the wealthy and the religious, by Express Mail from the Blacksburg post office just off campus. He listed his name on the package as "Ishmael."

He apparently began working on the materials at least six days before the massacre, NBC said. But some of his rantings were recorded after the first two slayings occurred around 7:15 a.m. in West Ambler Johnston Hall.

About 40 minutes after mailing the package, Cho was on the second floor of Norris Hall. There, he burst into crowded classrooms and began shooting students and teachers indiscriminately, many at powder-burn range. Then he killed himself.

Cho's mailing suggests he intended to be heard from beyond the grave.

Some of the video shows him talking from inside a car. At other times, he is shown in front of a cinderblock wall.

Karan Grewal, one of Cho's roommates, said that when he saw the footage, he could not believe it was the same person he had shared a six-person suite with since last fall.

"It was a totally different person," the 21-year-old accounting major said. "He was staring straight at the camera, and he never stared into our eyes or even looked at us."

Cho apparently sent some materials in PDF files and recorded others onto computer discs. According to NBC, the package included 27 QuickTime video files showing Cho talking into the camera. He does not direct his anger at any specific person but does mention "sin" and "spilling" his blood. He speaks at length about how much he loathes the wealthy. His voice often is soft and uneven, difficult to understand.

"I could have left," he says. "I could have fled. But no. I will no longer run. If not for me, for my children, for my brothers and sisters. I did it for them. ... The time came and I did it. I had to do what I did."

The son of parents who left a life of poverty in South Korea to run a dry-cleaning business and raise their children in Virginia, Cho turns his venom on people of privilege in the U.S.

"You had everything you wanted. Your Mercedes wasn't enough, you brats? Your golden necklaces weren't enough, you snobs? Your trust fund wasn't enough?"

He adds, "Thanks to you, I die like Jesus Christ, who inspired generations of the weak and the defenseless people."

It appears Cho spent some time putting the package together, said NBC News President Steve Capus. The shooter broke the video down into snippets that were embedded paragraph by paragraph into the main document.

In about a dozen of the photographs, Capus said, Cho aims handguns at the camera that are "consistent with what we've heard about the guns in this incident."