The Justice Department's internal investigator is poised to release a long-awaited report on Operation Fast and Furious that could answer some of the big remaining questions about the controversial Arizona gun-trafficking investigation.

Inspector General Michael Horowitz and his staff have taken more than a year to look into the operation, in which hundreds of guns were allowed to flow from Phoenix-area gun stores to suspected criminals in Mexico. If the current schedule holds, the report will be released before Horowitz testifies at a House Oversight Committee hearing on Tuesday (See story on C2).

The committee itself has issued several reports about Operation Fast and Furious, the most recent a 209-page account put out July 31. But in that report, the authors complain that congressional investigators have not had the same access to interview people or review documents that the inspector general had.

Now the many critics of the operation wonder if it will resolve any of the key questions on the gun-trafficking investigation that was revealed after the killing of Border Patrol Agent Brian Terry. On Dec. 14, 2010, the Tucson Sector agent was shot and killed west of Rio Rico, and the group of suspected bandits who shot at agents left two guns purchased by a Fast and Furious suspect.

In a written statement, U.S. Sen. Chuck Grassley, R-Iowa, who initially revealed the "gun-walking" aspect of Fast and Furious, said Terry's family members "deserve better than the treatment they've thus far received from the Justice Department.

"There are also some pretty heavy questions that have yet to be answered about who approved Operation Fast and Furious and who turned a blind eye and allowed the program to continue. These are important answers that will help us make sure something so stupid never happens again."

How high did knowledge of and responsibility for Operation Fast and Furious go?

It's a question that Terry's family has pressed as investigators for U.S. Rep. Darrell Issa, R-Calif., and Grassley probed Operation Fast and Furious.

The results so far: The highest Justice Department official who knew about so-called "gun-walking" in Arizona was Assistant Attorney General Lanny Breuer, the chief of the department's criminal division. However, what Breuer was learned of in April 2010 was Operation Wide Receiver, an earlier, Tucson-based investigation in which federal investigators also allowed traffickers to take guns across the border into Mexico while trying to bring down a group of gun-runners.

Grassley has called on Breuer to resign, in part because, even after Breuer learned of it, he did nothing to stop investigators from letting criminals traffic guns to Mexico.

The other high-ranking administration official to have learned of Operation Fast and Furious was Kevin O'Reilly, a national security staff member in the White House. Emails written in 2010 show that William Newell, then the special agent in charge of the Bureau of Alcohol, Tobacco, Firearms and Explosives' Phoenix office, told O'Reilly about Fast and Furious.

The administration refused to let congressional investigators interview O'Reilly.

For some conservative critics of the Obama administration, tying Operation Fast and Furious more directly to the White House is the dreamed-of objective. A group called The Conservative Caucus is offering a $100,000 reward for information showing that the White House was involved in Fast and Furious as an effort to further a gun-control agenda.

What's the responsibility of federal prosecutors in Arizona?

Investigations so far have revealed that one of the central problems that led to Fast and Furious was a misinterpretation of the gun-trafficking laws by the U.S. Attorney's Office in Phoenix.

Assistant U.S. Attorney Emory Hurley, the lead prosecutor in the case, insisted on a higher standard of proof than the law required, the July 31 congressional report says. It wasn't enough evidence of a crime, Hurley told agents during the investigation, that ATF agents saw suspects buy guns, swear on a form that they themselves were the intended customers, then immediately transfer them to other people.

"ATF had to have possession of the straw-purchased firearm" under Hurley's understanding of the law, "even if the whole reason for the prosecution was that the gun had been trafficked to Mexico following a straw purchase," the congressional report says.

The Justice Department refused to allow Hurley to speak with congressional investigators. The congressional committee subpoenaed his supervisor, criminal division chief Patrick Cunningham, but Cunningham asserted his Fifth Amendment right not to incriminate himself and refused to testify.

Their boss, then-U.S. Attorney Dennis Burke, resigned in August 2011 after interviews he gave to the Inspector General's Office in which he admitted leaking a document critical of a whistle-blower in the case.

What will the ultimate consequences be for the agents and attorneys involved?

Many of the ATF agents involved in the case have been reassigned, and the then-acting-director, Kenneth Melson, has resigned. But none has been fired.

Hurley was taken off the case but remains a U.S. Attorney's Office lawyer in the civil division.

It's one of the chief goals of Brian Terry's family to hold accountable those responsible for the ill-conceived investigation, said Robert Heyer, a cousin of Terry who has established a charity in his name, the Brian Terry Foundation.

"Supervisors in ATF, people in the U.S. Attorney's Office, and potentially supervisors in DOJ, you would think would need to be held accountable for the decisions made that put Americans at risk," he said while in Tucson last week.

But he warned, "The inspector general can only present findings and make recommendations. Ultimately the attorney general decides who is held accountable and in what manner."

Contact reporter Tim Steller at 520-807-8427 or tsteller@azstarnet.com