KANSAS CITY, Kan. (AP) — A federal judge is expected to hear testimony this week on whether prosecutors improperly used secret recordings of conversations between inmates and their attorneys at a federal prison in Kansas.

U.S. District Judge Julie Robinson scheduled a two-day evidentiary hearing on the court-appointed special master's findings concerning the government's failure to comply with the investigation and the appropriate response or remedies. The hearing begins Tuesday in Kansas City, Kansas.

More than 20 witnesses — including federal prosecutors and prison officials — have been subpoenaed to testify. Robinson appointed Ohio attorney David Cohen as the court's special master and in 2016 tasked him with independently investigating recordings at the Correction Corp. of America prison in Leavenworth.

Robinson has said that at the hearing, she also will consider any other issues the parties want to address related to the investigation. Federal Public Defender Melody Brannon asked Robinson last year to order the government to show why it should not be held in contempt for destroying evidence.

The government wiped clean the hard drive on the one computer dedicated to playing videos from the prison — after the court had ordered the government to produce all hard drives from the U.S. attorney's office. The move prevented the special master from potentially learning who viewed which recordings and when.

The investigation grew out of a prison contraband case during which criminal defense lawyers discovered that the prison was routinely recording meetings between attorneys and their clients.

Robinson subsequently expanded the probe to look into the conduct of federal prosecutors and staff, citing the government's lack of transparency about its possession, knowledge and use of recordings. She said she found that prosecutors have made inconsistent, inaccurate or misleading statements.

The investigation is now focusing on the question of whether the government intentionally viewed or listened to attorney-client conversations.

The government contends any interference in attorney-client communications must be purposeful for it to rise to a Sixth Amendment violation.

But Robinson has noted that "some evidence" already exists that the government purposefully obtained and used attorney-client communications related to criminal defendants.