Not being found guilty is not, by itself, enough to sue them, because the standard in a criminal case is so high ("proof beyond a reasonable doubt")--that fact that you were not convicted only means there wasn't enough evidence, not that the person filing charges acted maliciously or otherwise wrongfully. To successfully, sue, you'd need to be able to show that either this person specifically acted for improper reasons (e.g. not because he or she thought there was misconduct, but rather to punish you for something unrelated or extort you) and/or that no reasonable person could have *possibly* thought that there had been misconduct.