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CHICAGO -- An unprecedented hearing is underway today at the Dirksen Federal Courthouse.

A nine judge panel will decide if the Bureau of Alcohol, Tobacco, Firearms and Explosives used racial profiling in sting operations which led to the arrests and convictions of more than 40 Chicago area men.

The testimony, which is expected to last two days, will featuring two prominent expert witnesses.

One will be for the Chicago defendants hoping to have their charges thrown out, and a government expert who says race did not play a factor in the ATF's operations.

Taking the stand first today was defense expert Jeffery Fagan, a Colombia University Law School professor, who has testified in the past for both defense attorneys and on behalf of the government.

Fagan told the federal panel of judges there is a zero percent chance race did not play a factor in the ATF'S sting operations from 2006 to 2013.

ATF officers would create fake stash houses and entice suspects to rob the house.

When the suspects showed up, the officers would arrest them.

The suspects were supposed to be experienced robbers with violent pasts, but court documents show some had only minor convictions.

Fagan says the ATF used race as a factor to pick their suspects.

He studied 94 defendants in 24 separate stings over a 7 year period.

78% of suspects arrested were black.

The government's expert witness should testify this afternoon with closing arguments on Friday.

The decisions coming down in this case are not expected for months but could impact cases nationwide.