how long do i have for the police to charge me with a crime.

i was just notified that in 2010 i committed a crime of lewed behavior with a minor under the age of 14. they wanted to talk to me so i went and did a polygragh test and failed. i was acused of masterbating in front of this girl which i guess could be true because i was babtsitting her for my girlfriend in my own home when i did this. i also was accused of fondling her which could be true. she was 8 years old and learning how to ride a bike and she started to fall off. i caught her and my hand went across her chest. i never had any intention on doing anything sexual with this girl.