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Powell, 48, died in a cage last year after being exposed to the sun for nearly four hours. On May 19, 2009, the day she died, temperatures reached 107.5 degrees.

The corrections director, Charles Ryan, called has called Powell's death "unconscionable" and "an absolute failure."

The Department of Corrections disciplined 16 people in connection with the incident, with five employees fired or forced to resign.

Donna Hamm, executive director of Middle Ground, a prison-reform group, said a representative for Romley told her that attorneys who reviewed the case did not find enough evidence against a person or group of people that could guarantee a conviction.

Hamm, who said she has reviewed the 3,000-page report about Powell's death, said she believes statements from detention officers who walked by Powell and ignored her cries could have been enough to charge someone with negligent homicide.

She said was more troubled about the message detention officers could take from Romley's decision.

The Department of Corrections has put new policies in place since Powell's death that limit the amount of time inmates are detained in outdoor cages.

"All of these things that they're doing don't matter a whit unless the staff follows the policy," Hamm said. "Clearly prosecuting someone would send a very strong message, that the policy means something even if they didn't get a conviction. I think exactly the opposite message is communicated: that the staff can act with impunity against the inmates and there is no recourse."

The investigation into Powell's death showed that lengthy confinements in outdoor cages had become a common practice as officers tried to "wait out" prisoners who were agitated or refusing to return to their cells.

Vanessa Griego, a 24-year-old inmate, was confined to a similar cage at Perryville for 20 hours last year after refusing to return to her cell. She did not require medical attention, although the incident alarmed staff members and fellow inmates.

"Waiting out" prisoners meant corrections officers did not have to use force to return inmates to their cells. But it also meant inmates were regularly left outdoors for longer than the two-hour maximum dictated by prison policy.

The practice was discontinued as part of a series of reforms initiated in the wake of Powell's death.

Powell, who was serving a sentence for prostitution, said she felt suicidal at 11 a.m. on May 19. She was taken to the outdoor cage to await transportation for psychiatric care at the prison complex detention unit.

But the sergeant who saw Powell lose consciousness never reported the incident to supervisors, despite the fact that Powell said she was having trouble breathing, according to the subsequent investigation.

Powell, who struggled with mental illness, was taking psychotropic medications that made her particularly sensitive to the heat. But medical personnel did not share that information with corrections officers, according to the investigation.

At least 20 inmates told investigators that Powell was denied water for most or all of the time she was in her cage, despite regular requests. Those reports were bitterly disputed by corrections officers, who insisted that Powell was given water.

After more than two hours in the sun, Powell requested to be taken back to her indoor cell. But she was denied.

Powell also was denied a request to use the restroom and defecated in the cage. A corrections officer saw that Powell had soiled herself but left her where she was, according to the investigation. Medical personnel later found feces underneath her fingernails and all over her back.

The psychiatric unit to which Powell was awaiting transport should have accepted her hours before she died, the report found, but a series of miscommunications prevented her from being taken in.