how does piggy attempt to justify the murder of simon?

Piggy can't admit that the boys had killed Simon during frenzied lynching on the beach. Piggy's excuse was that it was an accident and that Simon had no business coming out of nowhere at night. The irony, of course, is that the boys mistake Simon for the beast. The reality is that they knew exactly who they were killing as Simon struggled to explain what he knew lay on the mountaintop. It is difficult to know if Ralph and Piggy were actually involved but they both witnessed what happened.