Terrill Thomas, 38, an inmate at the Milwaukee County Jail, was found dead in his cell on April 24, 2016.
Prosecutors say Thomas had been left alone for seven days without water, and the medical examiner's office says he died of "profound dehydration."
The District Attorney's Office is holding an inquest to determine whether a member of the jail staff should be charged in Thomas' death.
The Milwaukee Journal Sentinel reports:
"An inquest is a rarely used legal process that allows prosecutors to question witnesses under oath and in front of a jury before they file any criminal charges.
"The jury then returns a unanimous verdict as to whether there's probable cause to charge anybody, and what those charges should be. Prosecutors are not required to follow the jury's verdict."
Prosecutors said Tuesday that the jail's commander failed to inform police about the existence of surveillance video showing a guard shutting off water to the cell.
The Associated Press reports:
"A current and a former jail captain both testified Tuesday that the video showed a guard turning off water to the cell on April 17, shortly before Thomas was transferred there after he stuffed a mattress in a toilet to flood the cell he was previously in.
"Capt. George Gold testified that his jail commander, Nancy Lee Evans, directed him to review the video the day after Thomas died and report to her what he saw. Gold said after the guard turned off the water he didn't see anyone turn it back on.
"Gold said Evans 'was very surprised' to hear what the video showed. But when Evans took the stand later Tuesday she denied Gold ever told her about the water being shut off and said it was several months before she became aware that dehydration was the cause of Thomas' death.
"She denied withholding evidence, but [Assistant District Attorney Kurt] Bentley said Evans failed to direct staff to preserve the entire video and did not mention it to police until almost a year later."
Thomas was in jail after being arrested on charges that he shot a man and later fired two rounds inside a casino. Family members said he was suffering a mental breakdown.
Bentley said the evidence will show Thomas' bipolar disorder made it apparent he "was unable to tell people about his basic needs."
The inquest is expected to continue through at least the end of the week.