>>> u.s. attorney general eric holder became the first sitting cabinet official ever to be held in contempt of congress last night. tonight we'll take you inside the antigun running operation known as fast and furious that caused all the uproar to begin with. with the first television interview with the veteran atf agent who ran it, william newell , trying to penetrate a violent mexican drug cartel by tracking gun purchases, but the operation went wrong when a border patrol agent was killed and two guns from the operation were found at the scene. our national investigative correspondent michael isakoff has our exclusive report tonight.
>> to my knowledge not one fire arm was walked to a criminal intentionally.
>> reporter: in his first tv interview the agent in charge of operation fast and furious , an attempt to stem the tide of illegal guns to mexico , speaks out to clear the air about what he says really happened.
>> the notion that we somehow intentionally let guns walk is insane. never happened.
>> reporter: between mid 2009 and january, 2011 , atf agents watched as nearly 2,000 weapons were bought in arizona stores by suspected straw buyers, middle men believed to be purchasing the guns for someone else. newell was hoping to track the weapons to mexico 's most powerful drug organization.
>> to have the greatest impact in stopping what they were doing you have to cut off the head of the snake.
>> reporter: but the task of following the weapons proved daunting and went horribly wrong in december, 2010 , when u.s. border patrol agent brian terry was murdered in the arizona desert. two weapons found at the scene were guns that newell 's agents were tracking.
>> there was evidence that they knew that in fact weapons had already ended up in mexico . that's before brian terry was killed.
>> reporter: newell was at home when he got the call about terry.
>> it hit me very hard. it hit a lot of us in phoenix very, very hard.
>> reporter: newell believes he did everything he could, presenting evidence to federal prosecutors of hundreds of illegal purchases of guns, but was told he needed more evidence of the buyer's intent to charge them with a crime.
>> i think it is unconscionable the delay that occurred between august to january to bring charges against these individuals.
>> reporter: and that was the fault of?
>> the u.s. attorney 's office.
>> reporter: house republicans lay blame across the board.
>> one of the things that's so offensive about this case is that our federal government , knowingly, willfully, purposely gave the drug cartels nearly 2,000 weapons, mostly ak-47s, and allowed them to walk.
>> reporter: today newell says his career has been shattered and that field agents have been deterred from taking risks to stop gun trafficking for fear of being second guessed by congress.
>> not only mexico , the united states , the criminals have won. the people that are laughing all the way to and from the gun stores and to and from mexico are the criminals.
>> reporter: the justice department today declined comment but said in a letter to house speaker john boehner it will not prosecute the attorney general. michael isakoff, nbc news, washington.