CHARLESTON, W.Va. -- In the weeks before he was killed, the FBI was investigating Mingo County Sheriff Eugene Crum for laundering money by arranging to buy campaign signs with cash obtained from a doctor convicted of running a pill mill, according to a federal search warrant. According to the warrant, which was unsealed last week, Dr. Diane Shafer paid "hundreds of thousands of dollars in cash" to George White for making Crum's campaign signs, according to the warrant issued to search Crum's phone. The FBI also was investigating whether Crum committed mail fraud by submitting fake campaign disclosure forms by mail, and also if Crum possessed illegal drugs and if he intended to distribute those drugs. In September 2012, Shafer was sentenced to six months in jail after pleading guilty to misusing her Drug Enforcement Administration registration number. The plea came as a result of a federal probe that examined more than 118,000 prescriptions that Shafer doled out since 2003. Crum was shot to death on April 3 as he sat in his police cruiser in Williamson. The search warrant was filed May 7 and unsealed Friday. Recently, Crum and White were mentioned in a federal charge filed against Michael Thornsbury, who stepped down earlier this month as the county's only circuit judge before pleading guilty to conspiring to deprive White of his constitutional rights. Thornsbury's charge states that he, along with then-County Commissioner David Baisden and then-Prosecuting Attorney Michael Sparks, devised a scheme to keep White quiet about providing Crum with prescription pills. Federal agents wanted to search Crum's phone, because they believed there was evidence "of a conspiracy to tamper with an informant," according to the request for a search warrant. The request states that former Williamson police chief Dave Rockel participated in the scheme. Rockel stepped down as chief in June and joined the sheriff's department. However, he was fired last month by new Sheriff James Smith. Federal prosecutors said Crum had White arrested, instead of paying him $3,000 owed for campaign materials. Reportedly, White then went to federal agents and told them about allegedly providing Crum with pills. Agents then began investigating Crum on suspicion of mail fraud because of possible false campaign-finance disclosures, conspiracy to commit money laundering in connection with arranging for Shafer to purchase signs for his campaign with cash she received illegally, and unlawfully possessing controlled substances or intending to deliver controlled substances, the warrant states. Crum found out that White was talking to FBI agents, according to the warrant. To keep White quiet, county officials allegedly offered him a deal. If he switched to an attorney who was favored by Crum and Thornsbury, he would get a lighter sentence, according to federal prosecutors. White was sentenced to 1 to 15 years in prison on drug charges earlier this year. After Crum was shot and killed in April, he was remembered as a crusader who wanted to end the cycle of drug addiction in Mingo County. He started a crackdown, "Operation Zero Tolerance," which led to the indictment of 72 people on drug-related offenses and collected more than $75,000 in cash. Sparks also has been charged in connection to the alleged scheme. He faces a maximum of one year in jail for allegedly depriving White of his constitutional rights. He resigned as prosecutor and agreed to surrender his law license after he was charged. His lawyer has said Sparks plans to plead guilty. Baisden pleaded guilty to an unrelated federal charge and resigned earlier this month. Assistant U.S. Attorney Steve Ruby said Thursday that warrants are sealed to protect ongoing investigations. "Most of the information in this warrant application has now been made public in other cases," Ruby said. "When that occurs, it's part of our routine housekeeping to notify the court that the search warrant application can be unsealed." Reach Kate White at firstname.lastname@example.org or 304-348-1723.