Which bacteria killed the mice in Griffith’s transformation experiment?

In Griffith’s transformation experiment, the mice were killed by a combination of heat-killed virulent (smooth, encapsulated) Streptococcus pneumoniae and live non-virulent (rough, non-encapsulated) strains. The heat-killed virulent bacteria transferred their genetic material to the live non-virulent bacteria, enabling them to produce a protective capsule and become virulent, ultimately causing fatal pneumonia in the mice.