This is The Guardian.

Hi, it's Helen here.

We have something a little bit different for you today.

A weekend bonus, if you like.

It's the first episode of Off Duty,

a new series from Guardian Investigates.

It tells the story about how the brutal murder

of a Chicago cop spiraled into a 12-year hunt for justice.

You can find all of the rest of the series on the dedicated Guardian Investigates feed.

I hope you enjoy it.

Today and Focus will be back, as usual, on Monday morning.

On the evening of December 29, 2011, Clifton Lewis showed up for his shift at the M&M mini-mart 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

...