How does Felix frame Tony and Sebert?

Felix gives Lonnie and Sal sleeping pills, and while they are asleep, Tony and Sebert conspire to murder them, and to frame the prisoners, to make it look like they were killed in the prison riot. Or else, Tony says, they could make it look like Lonnie had a heart attack, since Tony says that he is “overdue for one” (228). Felix overhears all this, and records it by way of microphones hidden in the cell where they are kept.