This is The Guardian.

Hi, Pippa Carrera here, host of Politics Weekly.

You're about to hear episode one of a brand new series from Guardian Investigates,

all about a murder in Chicago and one man's 12-year fight to prove his innocence.

To hear the rest of the series, search for off-duty or Guardian Investigates wherever you listen to your podcasts

and hit subscribe. Hope you enjoy. On the evening of December 29th, 2011, Clifton Lewis showed up for his shift at the M&M mini-mark on Chicago's west side.

He worked days as an officer in the Chicago Police Department, but was moonlighting as a security guard to pick up a little extra cash.

He was chit-chatting behind the counter with the store owner and a clerk around 8.30 p.m.

When two men walked into the M&M.

They shot Lewis several times, then took off with his gun and police start.

Seconds after the gunmen left, a bystander called 911.

Lewis was rushed to the hospital.

More than 200 police officers gathered in the parking lot of Strosher Hospital where Lewis was pronounced dead.

He had been on the force for eight years, a black officer who lived in the neighborhood he served,

and he'd gotten engaged four days earlier on Christmas morning.

Police launched a massive manhunt for Lewis's killer.

The brass ordered that police were only this case until it was solved.

Tips poured in, and many pointed to the four-corner hustlers,

the gang that controlled the area around the mini-mart.

A week later, police had their suspects, but they weren't hustlers.

They were four men affiliated with the gang called the Spanish Cobra's.

For hours, under intense police questioning, they said they didn't do it.

...