Who killed Joffrey in the books?

Who killed Joffrey in the books? At the conclusion of the dinner, however, Joffrey dies from poisoned wine. Tyrion is falsely accused and arrested by Cersei in A Storm of Swords (2000) but it is later revealed that Lady Olenna Tyrell and Lord Petyr Baelish were the true perpetrators.

At the conclusion of the dinner, however, Joffrey dies from poisoned wine. Tyrion is falsely accused and arrested by Cersei in A Storm of Swords (2000) but it is later revealed that Lady Olenna Tyrell and Lord Petyr Baelish were the true perpetrators.