WASHINGTON (CNN) -- Attorney General Eric Holder said Monday that he found it "frustrating" that the Justice Department hasn't been able to carry out criminal prosecutions of executives whose risky banking practices blamed for the global financial crisis.

As Holder wraps up nearly six years at the helm of the Justice Department, the attorney general has drawn criticism for his department's record on white collar crime.

Some critics say the department failed by not bringing charges as a deterrent against shoddy practices on Wall Street. Some fault him for instead extracting billion dollar settlements from the world's biggest banks.

Holder has defended the department's record saying the settlements are one way to prod shareholder to hold management more accountable.

Still, in an exclusive interview with CNN on Monday, Holder acknowledged that the lack of criminal prosecutions of executives "is something that is frustrating."

"The American people should understand we looked at those matters, tried to come up with ways in which we could hold people and institutions accountable," Holder told CNN. "We have prosecuted certain institutions. We have gotten record amounts of money in and we've used that money for appropriate remedial measures so that people can stay in their houses, have their mortgages reduced. So a lot of good has come from our efforts in that regard."

Holder noted that he has called for Congress to change federal law to encourage white collar whistleblowers from inside Wall Street to help the Justice Department bring cases.

There are, he said, "a number of measures that I think Congress might change so that the prosecution of these kinds of cases is not as difficult as they are."

Here are other things we learned from the interview:

1. There are "about a dozen" American jihadists in Syria and Iraq.

That, at least, is "our estimate now," Holder said. He said the government has "dozens of investigations that are underway about other people who have either gone or are planning to go."

"So this is something that is a priority for us on -- at the Justice Department and at the FBI, working in conjunction with our U.S. attorneys, where we're trying to engage in preventive activities as well," he said.

2. He won't write a book critical of Obama while the president's in office.

Former Defense Secretary Leon Panetta criticized Obama's decision-making ability, especially in entanglements such as Syria, in a recently-published book. Holder said Panetta's comments were "unfortunate" -- and that he should have waited.

"Frankly, I don't think it's something that a former cabinet member should do while the president he served is still in office," Holder said. "That's not something that I would even consider doing."

3. He's disappointed that gun control measures haven't become law.

Holder said he takes it "personally as a failure" that Congress didn't react to shootings like the one in Newtown, Connecticut, by changing U.S. gun laws. "The inability to pass reasonable gun safety laws after the Newtown massacre is something that weighs heavily on my mind," Holder said.

4. But he counts gay rights and voting rights efforts as important successes.

He listed knocking down the "final vestiges of discrimination" on those issues among the first of "a whole variety of things that I'm really proud of the people of this Justice Department and the way they've done them over the past six years."

Also on that list: Criminal justice reforms; record settlements with financial institutions; and "the work we've done in the national security sphere."

5. Holder is watching Missouri before making a decision on charges in the Michael Brown shooting.

He said if Darren Wilson, the officer who shot and killed Brown in Ferguson, isn't indicted, he'd first want to see whether Missouri's efforts were "adequate."

"I think what we'll have to do, as we always do in a civil rights investigation from a federal perspective, is look at what the state has done and then make a determination as to whether or not the state investigation was adequate," Holder said.

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