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The chief of the Bureau of Alcohol, Tobacco, Firearms and Explosives was re-assigned today as controversy grows concerning Operation Fast and Furious.

Questions remain about how much the chief, Kenneth Melson, and other officials, knew about a botched attempt to track firearms circulating to drug cartels in Mexico.

According to a Reuters story, the "Fast and Furious" operation:

"Has spawned congressional and internal Justice Department probes and put the Obama administration on the defensive about whether dangerous weapons were knowingly allowed to cross the border.

"Republicans in the U.S. Congress have been demanding the Obama administration explain who knew what and when about the ATF program, which was conceived of and run out of the agency's Phoenix division."

According to USA Today, the gun-trafficking investigation is looking into whether hundreds of firearms fell into the hands of Mexican drug cartel enforcers and criminals in the US. 

Melson will be replaced by B. Todd Jones, the top federal prosecutor in Minnesota. 

Melson steps down to take the position of senior adviser on forensic science in the Department of Justice's Office of Legal Programs.

The U.S. attorney for Arizona, Dennis Burke, has also resigned.

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