A 58-year-old man with a 10-year history of chronic hepatitis C presents with progressive liver dysfunction. A liver biopsy shows extensive hepatocyte apoptosis with numerous Councilman bodies (apoptotic hepatocytes). Immunohistochemistry demonstrates increased infiltration of CD8+ T lymphocytes in the portal tracts and lobules. Serum transaminases are markedly elevated (ALT 320 U/L, AST 380 U/L). The pathologist notes that the pattern of cell death is consistent with cytotoxic T lymphocyte-mediated apoptosis. Which of the following best describes the primary molecular mechanism by which these CD8+ T cells are inducing hepatocyte death in this patient?