Washington (CNN) Three times in total in the last month, the Justice Department and the FBI heard from top intelligence community officials about President Donald Trump's call with the Ukrainian president.

Those referrals prompted prosecutors to consider whether to open a full-blown campaign finance criminal investigation. DOJ decided not to, yet the intelligence community's inspector general and the Director of National Intelligence had thought the whistleblower's allegation was credible enough to seek legal backup.

So what happened?

The information in the Justice Department moved quickly beginning at the end of August. Two weeks after Intelligence Community Inspector General Michael Atkinson received the whistleblower's complaint about Trump's July phone call, he notified his superior, the acting Director of National Intelligence Joseph Maguire. Atkinson believed it to be a credible complaint and found it worthy to be handled by the intelligence community and referred to Congress under the law.

But instead of the route to Congress, the whistleblower's allegation wound its way across the Justice Department.

In that final week of August, Maguire's team reached out to the Justice Department. The intel office had a question for Justice's Office of Legal Counsel on whether the office needed to alert Congress. That was the first time DOJ was alerted about the situation, senior officials said. The Office of Legal Counsel later said the complaint could be looked at as a possible criminal matter, sending it along to the department's Criminal Division, according to a legal memo released Wednesday.

Around the same time, Atkinson, who had first heard from the whistleblower, also referred the matter to the Justice Department.

Together, those notifications kicked off the Justice Department's probe of whether there was a possible violation of a campaign finance criminal statute.

Justice's Criminal Division took the lead. Prosecutors obtained the summary transcript of the call from the White House, and prosecutors confirmed with knowledgeable people at the White House that the five-page document was the best evidence available, according to the officials. They did not interview any to gather more facts.

On the day after Labor Day, the Office of Legal Counsel had its answer for Maguire. The whistleblower's complaint shouldn't be considered of "urgent concern" and require disclosure to Congress, Steven Engel, the assistant attorney general for the Office of Legal Counsel wrote.

Engel reasoned that preventing foreign campaign contributions that could influence an election was not in the "operational responsibility" of the Director of National Intelligence. The DOJ also noted that the President is not a member of the intelligence community, and Trump's phone call itself wasn't an intelligence activity.

"The [whistleblower] complainant describes a hearsay report that the President, who is not a member of the intelligence community, abused his authority or acted unlawfully in connection with foreign diplomacy," Engel wrote. But the whistleblower's allegations "do not arise in connection with any such intelligence activity at all" that's handled by the Office of the Director of National Intelligence.

The follow day, September 4, inspector general Atkinson spoke up again, this time to the FBI. With the Criminal Division at work, the FBI deferred to the prosecutors.

Two more weeks went by, with career public integrity prosecutors looking at the matter, according to the officials. Then sometime last week, the Justice Department made its final determination: no reason for a full-blown criminal investigation. What the President asked of Ukrainian President Volodymyr Zelensky couldn't amount to a quantifiable "thing of value" under campaign finance law, top administration officials determined.

Criminal Division assistant attorney general Brian Benczkowski made the final call, the senior DOJ officials said. The Office of Deputy Attorney General Jeffrey Rosen was also involved with the legal analysis, as were the heads of the National Security Division and the Office of Legal Counsel, the officials said.

"All relevant components of the Department agreed with this legal conclusion," Justice Department spokesperson Kerri Kupec said.

Attorney General William Barr, for his part, had "minimal involvement" in the Justice Department's handling of the referral, an official briefed on the matter said.