Police said material seized from the computer of Pekka-Eric Auvinen suggests the 18-year-old had had Internet contacts with Dillon Cossey, 14, who was arrested in October for allegedly preparing a possible attack at Plymouth Whitemarsh High School in Pennsylvania.
"I consider it quite possible that he has been in contact" with Cossey, Det. Supt. Rabbe von Hertzen told The Associated Press.
He declined to provide details saying the investigation was on going.
Auvinen killed six students, a nurse and the principal in a high school shooting spree Wednesday in Tuusula, about 50 kilometers (30 miles) north of the Finnish capital, Helsinki. He then shot himself in the head, and died hours later at a hospital.