MILWAUKEE — A special prosecutor on Friday declined to charge three Milwaukee police officers in whose custody a gasping suspect died in 2011, saying there wasn’t enough evidence to prove a case beyond a reasonable doubt.

Derek Williams, 22, died after struggling to breathe in the back of a squad car in July 2011. He pleaded with the officers to roll down a window and call an ambulance but one unidentified officer replied, “Nope, you’re talking to me, you’re just playing games,” according to a transcript of the squad-car video.

Last month an inquest jury found probable cause to support charges against the three officers of failure to render aid. But special prosecutor John Franke said he didn’t file charges because he wasn’t confident he could meet the higher standard of proving guilt beyond a reasonable doubt.

Specifically, he would have had to prove the officers believed medical attention was needed and that they knew failure to obtain aid would cause bodily harm, he wrote in a 33-page report released Friday.

“The evidence is clearly insufficient to satisfy that burden of proof as to any one of these three officers,” Franke said.

He said the officers’ failure to act was a “grievous mistake,” but that charges would have to reflect criminal intent, not just a failure to do what “should have been done.”

Franke declined to comment to The Associated Press beyond what was written in the report.

The officers — Jason Bleichwehl, Jeffrey Cline and Richard Ticcioni — declined to testify during the inquest, citing their Fifth Amendment right against self-incrimination. Other officers testified that they thought Williams was faking.

The inquest jury found probable cause that Williams — who had a genetic marker for sickle cell but not the disease itself — died of sickle-cell crisis.

The lawyers for Bleichwehl and Ticcioni did not immediately return messages Friday. Cline’s attorney, Bridget Boyle, said her client was upset about Williams’s death but not criminally liable.

“Milwaukee police officers are not taught how to identify who has sickle-cell trait or how to assess people for sickle-cell trait,” she said. “This is an unfortunate, unfortunate circumstance but I think the right decision was made by Franke.”

The medical examiner’s office initially ruled Williams died of natural causes. But the Milwaukee Journal Sentinel later obtained the squad-car video — which shows Williams pleading for help from the back seat for nearly eight minutes and growing progressively weaker until he collapses on his side — the medical examiner’s office changed the manner of death to homicide.

Franke said the squad-car video was filmed using an infrared camera that produces a clearer image than what police would have seen on that dark night, perhaps with glare from their laptops reflecting on the plastic window between the front and back seats.

“It is unfair to judge the officers’ state of mind based on the videotape, which was simply not a part of the information used by the officers in deciding whether to believe Williams,” the report said.

Milwaukee County District Attorney John Chisholm, who initially concluded that police had done nothing wrong, asked Franke, a private attorney, to serve as the special prosecutor.

Chisholm released a statement Friday asking the community to respect Franke’s thought process and final decision.

In his closing statement to the inquest jury, Franke presented arguments both in favor of charges and against charges. On one hand, he said, half a dozen neighbors testified that they heard Williams repeatedly saying he couldn’t breathe as he was arrested and taken to the squad car. On the other hand, the officers eventually performed CPR and called paramedics, Franke said.

Franke earlier decided against asking the inquest jury to consider felony homicide charges against the officers because of the complexity of the medical evidence and lingering uncertainty about why Williams died.

Williams was arrested after running about a block and a half. He had been released from jail earlier in the day, where he had been held for unpaid tickets. Nothing in the jail records indicated any medical problem, and family members who’d had regular contact with Williams prior to his death didn’t see or hear anything that suggested any medical issues, Franke’s report said.

The inquest jury was asked to weigh in on a possible misdemeanor charge of failing to render aid. The charge would have carried a maximum sentence of nine months in jail and a $10,000 fine.

The girlfriend, Sharday Rose, told AP she was angry that Franke wasn’t bringing charges. Later, after noting that even if the officers were charged and convicted they’d be free within a year, Rose said she was more angry at a legal system that wasn’t producing accountability.

“I feel like they should not be back working on the streets after they let him die,” said Rose, 24.

Rose and Williams had three kids — two daughters ages 4 and 2 and a 3-year-old son.

“My kids need some justice,” she said.

The officers could still face federal criminal charges. The U.S. Attorney’s office in Milwaukee has not ruled out charging the three officers, and the U.S. Department of Justice is considering whether to sue the Milwaukee Police Department over a possible pattern of civil rights abuses.

“A decision has not been made,” U.S. Attorney James Santelle said. “I can tell you there’s nothing imminent right now.”

The Milwaukee Journal Sentinel has posted the police video here: http://bit.ly/10kU9SX