Blacksburg, Va. —The investigation of the Virginia Tech shootings has increasingly focused on the computer and cellphone activities of the shooter, Seung-Hui Cho. On Saturday investigators revealed that in March he purchased empty ammunition clips on eBay, the Internet-based auction service.

Using an account named blazers5505, Mr. Cho bought five clips for the two handguns used in the massacre, the Associated Press reported. The transactions were apparently legal.

Mr. Cho was a regular eBay user, according to news accounts, selling tickets to basketball and football games at Virginia Tech, and also books related to his English classes, including one course called “Contemporary Horror.” One of the books he sold was Men, Women, and Chain Saws: Gender in the Modern Horror Film, by Carol J. Clover, a professor of film studies, rhetoric, and Scandinavian at the University of California at Berkeley (Princeton University Press, 1992).

In addition to examining Mr. Cho’s computer activities, investigators are reportedly seeking his cellphone records, apparently in an effort to determine his motive for the attacks, in which he killed 32 students and faculty members, as well as himself. —Paul Fain