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CLAY COUNTY, Mo. — It’s possible a registered sex offender accused by Clay County authorities of coaching a youth basketball team in violation of state law may not actually be doing anything illegal.

Darin Mason has been on the Missouri sex offender registry for more than a decade and for the past nine years he’s been coaching a youth basketball team in Platte County with apparently no interference from authorities.

Because Mason coached games across the county line in Liberty, Clay County is now trying to keep him from coaching but the law they are using seems to be up for interpretation.

Mason pleaded guilty in 2001 to having sex with a 15-year-old girl on his Oak Park High basketball team. Over the years parents have brought Mason’s sex offender status and his job as a coach to the attention of police and prosecutors in Platte County.

FOX 4 asked why prosecutor Eric Zhand never brought charges, he declined comment. But in 2011, when asked the same question by the Kansas City Star, Zahnd said prosecutors have had a hard time applying 2009 legislation prohibiting sex offenders from serving as an athletic coach, manager or trainer for youth retroactively. Meaning Mason’s guilty please came before the law. Local criminal defense attorney David Langston, who’s not involved with the case weighed in on Wednesday.

“I believe that Eric Zahnd in Platte Co. does believe that the statute is not applicable because of the Phillips case, Doe v Phillips which makes it retroactive which they say is not appropriate, not legal,” said Langston.

And while Zahnd may be right, Clay County Prosecutor Dan White’s spokesman Jim Roberts says they believe they have a case and are going to try. A move Langston agrees with.

“I believe that according to the law …. the simple answer to that is no. And I believe that the overlay of the federal law over the state law, that you must register, and from what vie reviewed and the information that I have, he signed a new agreement when he registered the last time,” Langston said.

According to court documents, a year ago Mason signed an agreement saying he would not coach youth under the age of 17. But according to Clay County he did anyway. Now it may be up to a judge to decide if that’s in Mason’s legal rights.

Mason’s felony charge is punishable with up to four years in prison.

Mason is currently out on bond.