Inside the nighttime hunt for ISIS suspects in Iraq

In Iraq, Kurdish Peshmerga fighters hunt down terror suspects every day, although almost always at night.

The squads CBS News correspondent Charlie D'Agata and his team joined Monday night were going after suspects from one of the worst Islamic State of Iraq and Syria (ISIS) atrocities Iraq has seen.

CBS News met Gen. Sahed Khaled Mohammed and his men at a secret location south of Kirkuk. He told us they were after four ISIS suspects, a sleeper cell lying low among the local population, plotting terror attacks in Iraq.

Down a muddy road, they nab the first one. He didn't put up any resistance. But in the back of the truck, it's starting to sink in.

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The targets: Men suspected of taking part in the massacre of as many as 1,700 army recruits when ISIS overran a military base in Tikrit last year, where they were lined up by the hundreds and shot dead in shallow graves. The general said the men they were after were among those who pulled the trigger.

The next location was a warehouse, where they hoped to find three other suspects.

But they only found one.

He too is blindfolded and taken away for interrogation. Two more men from the suspected terror cell are still at large, and they now know their cohorts have already been taken in.

The general told us because they hide in plain sight and then strike civilian areas, the terror suspects he hunts down every week pose more of a threat than ISIS militants his forces face on the front lines.