Secret 

"There are three murderers hiding in your midst." These are the ominous words given to the six survivors of a tragic bus accident, followed by an ultimatum: Within one week, the murderers must anguish over their crimes and find some way to answer for them, or the evidence of their sins will be given to the police. But when every person has a secret, who can you trust…? (Source: Yen Press) Includes a bonus chapter.