Murder, thievery, muggings, rape, and so much more go on on a daily basis. Many of these crimes go unpunished for days, weeks, months, even years. Sometimes the offender is never brought to justice before they die happily in their bed of old age. With this in mind, no, I don't believe karma exists. Life is far too picky in who it decides get punished for their crimes and who is rewarded for their good deeds for me to have any reason to.