In June 2017, a Santa Fe County grand jury charged Griego with 22 criminal counts related to his campaign finance reports. Griego allegedly used his campaign funds for personal use and lied about it. Of the 22 charges, Griego was charged with "13 felony perjury counts; five felony counts of embezzlement; a felony fraud count; two misdemeanor counts of filing false campaign reports; and a misdemeanor count of illegally paying a Santa Fe auto repair shop with campaign funds." He pleaded not guilty to the charges.

On March 14, 2015, Griego resigned in the wake of an ethics investigation by an interim legislative ethics committee. The subject of the investigation was Griego's involvement in a 2014 real estate deal in which the legislature approved the sale of a state-owned building. Not long after that, Griego said he was contacted by the building's buyer and was made broker of the building. He reportedly made a $50,000 commission on the sale. When asked about the property deal last year, Griego told the Albuquerque Journal, "I didn’t feel there was an ethical problem when I did the deal. We were already out of the session. I didn’t feel I was doing anything wrong." The state's Constitution prohibits lawmakers from financially benefiting from any contract passed by the Legislature during their term in office. According to the New Mexico Political Report, a Senate member said that Griego had two options when the ethics investigation became public: "[t]he choice was resignation or a possible vote on removal from office." On February 29, 2016, the New Mexico Attorney's General Office charged Griego with nine criminal counts over his involvement in the sale of a state-owned building. The nine criminal counts include: 3 counts of fraud, 1 count of perjury, 1 count of tampering with public records, 1 count of financial disclosure violations, 1 count of bribery and solicitation and 2 counts of "violating the ethical principles of public service." According to the complaint, Griego earned more than $50,000 in commission from the sale, but he failed to disclose it, which is required by state law. He also failed to disclose his interest in the deal when it was discussed in the legislature. Griego has denied any wrongdoing and has vowed to fight the charges. On April 4, 2016, Griego pleaded not guilty to the charges. After a number of delays, the four-day hearing began on July 5, 2016. On July 8, 2016, District Judge Brett Loveless ruled that there was enough probable cause for Griego to face trial on nine charges. One felony fraud count was dismissed before the trial. The trial began on October 30, 2017. On November 16, 2017, Griego was found guilty on five of the eight charges in the corruption trial. He was found guilty of one charge each of fraud, bribery, and having an unlawful interest in a public contract. He was also found guilty of two counts of ethical violations. On February 16, 2018, Griego was sentenced to 18 months in prison and more than $47,000 in fines. He was also sentenced to five years of probation upon his release from prison and ordered to complete 1,000 hours of community service.

Opponent Jack Sullivan filed a complaint with the New Mexico Secretary of State against Griego alleging that he was misusing campaign funds. He responded in particular to one claim about a 1955 Chevy truck he used, saying the truck was used solely by the campaign. The Secretary of State approved Griego's expense of the truck.