The student killed two people in a dorm room, returned to his own dorm room where he re-armed and left a “disturbing note” before entering a classroom building on the other side of campus to continue his rampage, sources said.

Cho’s identitiy has been confirmed with a positive fingerprint match on the guns used in the rampage and with immigration materials. It is believed that he was the shooter in both incidents yesterday. Sources say Cho was carrying a backpack that contained receipts for a March purchase of a Glock 9 mm pistol, sources said. Witnesses had also told authorities that the shooter was carrying a backpack. Sections of chain similar to those used to lock the main doors at Norris Hall, the site of the second shooting that left 31 dead, were also found inside a Virginia Tech dormitory, sources confirmed to ABC News.

In all, the massacre at Virginia Tech left 33 people dead — including Cho himself — in the worst shooting in modern American history.

President Charles Steger told “Good Morning America’s” Diane Sawyer that police were still investigating the possibility of a second shooter, and said authorities had already interviewed one “person of interest.”

“There may be others,” said Steger, who will join the Virginia Tech chief of police at a press conference Tuesday morning. “We just don’t know.”