Days after the authorities in Minnesota announced that no one would be criminally charged in the 2016 overdose death of Prince, his next of kin are suing an Illinois hospital that treated the singer for an opioid overdose the week before his fatal incident, according to a suit filed on Monday.

Prince’s family, under the name of a trustee, Michael A. Zimmer, charge in the suit that the singer received improper medical care in the early morning hours of April 15, 2016, after Prince’s private plane made an emergency landing in Moline, Ill., following a show in Atlanta.

The suit claims that Prince’s death was a “direct and proximate cause” of the hospital failing to appropriately diagnose and treat the overdose, as well as its failure to investigate the cause and provide proper counseling.

Based on documents related to the criminal investigation released on Friday, prosecutors believe that Prince had likely overdosed that night on what he believed to be prescription opioids like Vicodin, but were actually black market versions containing the much more powerful synthetic opioid fentanyl. Authorities determined that, without knowing, Prince most likely took a counterfeit drug containing fentanyl again six days later at home in Paisley Park, leading to his death at 57.