For some crimes the perpetrator can be detected costlessly but can only be apprehended at significant cost, or not at all for some period of time. To deter strategic behavior in the period between detection and apprehension, authorities may wish to commit themselves to punishing the criminal once apprehended, regardless of the perpetrator’s behavior or threats. However we show that such efforts at commitment to ex post punishment may induce worse behavior and that it selects potential criminals of a worse type. We show that when law enforcement authorities cannot commit themselves perfectly, it is dangerous for them to try to commit as it may invoke a strategic response that can worsen the situation. When law enforcement authorities do increase their commitment to punish such offenders, it is likely to lead to less but more gruesome crimes.