a wreck is probably a little different, but from talking to people the general consensus seems to be that you could commit murder and get off as long as the cop that arrested you isn't at court... i don't know the technicalities if there are any, but i'd imagine theres some cases, like an accident, where some testimony is necessary, where in a speeding case even with out the ticketing officer the judge will have a sheet that says "80 in a 55" or something and shouldn't have any trouble having his way with you on that alone with out the officer present