Grand jurors investigating the Tulsa County Sheriff's Office took a tour of the county jail Tuesday.
Grand juries are required by state law to visit the jail at least once during their term.
Sheriff's office spokesman Terry Simonson said the tour started around 10:30 Tuesday morning and lasted about two and a half hours.
He said afterwards the grand jury heard testimony from witnesses and will hear more Wednesday.
The sheriff's office came under scrutiny after the April 2 shooting death of suspect Eric Harris by Reserve Deputy Bob Bates.
Bates goes on trial for second-degree manslaughter in February.
Meanwhile, former sheriff's office spokesman Shannon Clark said he was wrongfully fired after the shooting, in what he believes was an effort to insinuate he's to blame for problems within the office.
Clark said he was a loyal employee and is looking forward to testifying before the grand jury.