In order to win a lawsuit for defamation, the plaintiff must prove that the defendant made false statements about him to a third party, and that his reputation was damaged as a result.
There is, however, protection against defamation lawsuits for people who report something to the police in good faith. The key there is the term good faith. If the police report was knowingly false, then there is no protection for the party making their report.
In addition, the party making a false police report may be liable for abuse of process. Abuse of process occurs when a person harasses another person by knowingly filing a false police report or otherwise lies to get somebody in trouble with the law.
You haven't provided me with nearly enough facts to say whether you have a reasonable chance of winning, however. But hopefully the information above will help you to determine how to proceed.
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