The Maricopa County Attorney's Office has declined to pursue criminal charges in the death of Marcia Powell, a state prison inmate who died of heat-related causes after being left in an outdoor cage for hours.

The Department of Corrections had recommended that seven corrections officers on duty that day be charged with negligent homicide in connection with Powell's death. But there was not enough evidence to prosecute them, said Paul Ahler, chief deputy prosecutor.

Powell, 48, died last year after being exposed to the sun for nearly four hours at Arizona State Prison Complex-Perryville in Goodyear. On May 19, the day she died, temperatures reached 107.5 degrees.

Corrections Director Charles Ryan has called Powell's death "unconscionable" and "an absolute failure."

In a brief statement Wednesday, Ryan said he accepted the county attorney's decision.

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

But a four-month investigation of the incident by the department last year failed to answer several key questions, including how much water Powell received while in the enclosure, and when and how she succumbed to the heat.

Moreover, investigators could not determine how the actions or inactions of the corrections staff contributed to the delay of discovering that Powell was in distress and on the verge of death.

"We really did spend a lot of time and man-hours looking at this in an effort to see if we could patch together a case that we could prove," Ahler said. "We just felt at the end of the day, we didn't have enough to do that."

Ahler was chairman for the committee that reviewed the investigation. Incident-review teams met five times over the past year in an effort to build a case.

Donna Hamm, executive director of Middle Ground, a prison-reform group, said statements from officers who walked by Powell and ignored her cries could have been enough to charge someone with negligent homicide.

Hamm said she was more troubled about the message corrections officers could take from the county attorney's decision, despite new policies being put in place to 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."

Hamm said she planned to contact the U.S. Department of Justice to see if it is willing to review the case.

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.

Inmate Vanessa Griego, 24, 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.

The sergeant who saw Powell lose consciousness never reported that to supervisors, despite the fact that Powell said she was having trouble breathing, 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 officers, who insisted that Powell was given water.

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

Powell also was denied a request to use the restroom and defecated in the cage. An officer saw that Powell had soiled herself but left her where she was, the investigation found. 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 said, but a series of miscommunications prevented her being taken in.

The Corrections Department had recommended negligent-homicide charges against seven corrections officers: Esmeralda Pegues, Evan Hazelton, Iain Fenyves, Electra Allen, Cortez Agnew, Anita Macias and Ariana Mena.

A presentation to the County Attorney's Office said the officers were "negligent in providing the appropriate shade and water a reasonable person should have known needed to be provided" to a person in Powell's situation.

Republic reporter JJ Hensley contributed to this article.