LITTLE ROCK—The Arkansas Supreme Court overturned the corruption conviction of a former Lonoke police chief on Thursday, saying a prosecutor took a random set of allegations and wrongly concluded that Ronald Jay Campbell conducted a continuing criminal enterprise in the town.

Prosecutors failed to present substantial evidence to support a conviction, justices said in a unanimous order sending the case back to Lonoke County. The court also said lurid trial testimony that Campbell’s wife had sex with state prisoners at the local jail kept him from receiving a fair trial. Justices also said a search warrant used to obtain evidence was defective.

Campbell was sentenced to 40 years after being convicted on 23 counts including masterminding a criminal enterprise and a series of underlying crimes ranging from obtaining drugs by fraud to hindering prosecution. His wife, Kelly, was sentenced to 20 years after being convicted on 26 underlying crimes, including burglary and helping an inmate escape. She was acquitted on a charge that she took part in a criminal organization with her husband and others.

Prosecutor Lona McCastlain obtained a 78-count indictment against six people in 2006. The arrests rattled the town of 4,300, with claims that the chief conspired to make methamphetamine and that his wife provided marijuana and alcohol to inmates, and took prisoners to her husband’s office for sex.