WASHINGTON (AP) — The search of former President Donald Trump' s Mar-a-Lago club for classified documents and other government records may have come as a surprise to the public. But new legal filings show the investigation that triggered the unprecedented action was months in the making. The documents make clear that Trump had ample opportunity to return the material the government requested —- and then subpoenaed — and reveal the sheer quantity of highly sensitive documents he was keeping at the club.

A timeline of notable developments:

JAN. 20, 2021

Then-President Donald Trump left the White House for Florida ahead of President-elect Joe Biden's inauguration. According to the General Services Administration, members of Trump's transition team were responsible for packing items into boxes, putting boxes on pallets and shrink-wrapping those pallets so they could be transported.

Prior to shipping, GSA said it "required the outgoing transition team to certify in writing that the items being shipped were required to wind down the Office of the Former President and would be utilized as the Office transitioned to its new location in Florida."

GSA did not examine the contents of the boxes and "had no knowledge of the contents prior to shipping," according to an agency spokesperson. GSA was also not responsible for the former president's personal belongings, which were transported by a private moving company.

Under the Presidential Records Act, presidential records are considered federal property — not private — and are supposed to be turned over to the National Archives and Records Administration. Multiple federal laws govern the handling of classified and sensitive government documents, including statutes that make it a crime to remove such material and retain it at an unauthorized location.

MAY 2021

After NARA realized that documents from Trump's presidency seemed to be missing from the material that it received as he left office, the agency requested the records from Trump on or about May 6, 2021, according to a heavily redacted affidavit made public last week.

DECEMBER 2021:

NARA "continued to make requests" for records it believed to be missing for several months, according to the affidavit. Around late December 2021, a Trump representative informed the agency that an additional 12 boxes of records that should have been turned over had been found at the former president's Mar-a-Lago club and residence and were ready to be retrieved.

JAN. 18, 2022

NARA received 15 boxes of presidential records that had been stored at Mar-a-Lago — 14 of which, it would later be revealed, contained classified documents. The documents were found mixed in with an assortment of other material, including newspapers, magazines, photos and personal correspondence.

In total, the boxes were found to contain 184 documents with classified markings, including 67 marked confidential, 92 secret and 25 top secret. Agents who inspected the boxes also found special markings suggesting they included information from highly sensitive human sources or the collection of electronic "signals" authorized by a court under the Foreign Intelligence Surveillance Act.

FEB. 9, 2022

The special agent in charge of NARA's Office of the Inspector General sent a referral to the Justice Department via email after a preliminary review of the boxes revealed numerous classified documents.

"Of most significant concern," they wrote, according to a heavily-redacted affidavit released last week, "was that highly classified records were unfoldered, intermixed with other records, and otherwise unproperly (sic) identified."

After an initial review of the NARA referral, the FBI opened a criminal investigation into the matter.

FEB. 10, 2022

Trump's Save America PAC released a statement insisting the return of the documents had been as "routine" and "no big deal."

Trump insisted the "papers were given easily and without conflict and on a very friendly basis," and added, "It was a great honor to work with NARA to help formally preserve the Trump Legacy."

FEB. 18, 2022

NARA revealed in a letter to a congressional oversight committee that classified information was found in the 15 recovered boxes and confirmed the Justice Department referral.

Trump's Save America PAC released another statement insisting, "The National Archives did not 'find' anything," but "were given, upon request, Presidential Records in an ordinary and routine process to ensure the preservation of my legacy and in accordance with the Presidential Records Act."

APRIL 12, 2022

NARA informed Trump of its intent to provide the documents to the FBI, at the request of the Justice Department. A Trump representative requested an extension until April 29.

APRIL 29, 2022

The Justice Department sent a letter to Trump's lawyers seeking immediate access to the material, "citing "important national security interest."

"Access to the materials is not only necessary for purposes of our ongoing criminal investigation, but the Executive Branch must also conduct an assessment of the potential damage resulting from the apparent manner in which these materials were stored and transported and take any necessary remedial steps," the department wrote.

Trump's lawyers requested an additional extension.

MAY 10, 2022

NARA informed Trump's lawyers that it would provide the FBI access to the records as soon as May 12.

MAY 11, 2022

The Justice Department issued a subpoena for additional records.

JUNE 3, 2022

Three FBI agents and a DOJ attorney went to Mar-a-Lago to collect additional material offered by a Trump attorney in response to the subpoena. They were given "a single Redweld envelope, double-wrapped in tape, containing the documents," according to an Aug. 30 filing.

That envelope, it was later found, contained 38 documents with classification markings, including five documents marked confidential, 16 marked secret and 17 marked top secret.

During the visit, the filing said, "Counsel for the former President offered no explanation as to why boxes of government records, including 38 documents with classification markings, remained at the Premises nearly five months after the production of the Fifteen Boxes and nearly one-and-a-half years after the end of the Administration."

Trump's lawyers also told investigators that all of the records that had come from the White House were stored in one location — a Mar-a-Lago storage room. Investigators were permitted to visit the room, but were "explicitly prohibited" from opening or looking inside any of the boxes, they reported, "giving no opportunity for the government to confirm that no documents with classification markings remained."

The Justice Department was also given a signed certification letter stating that a "diligent search" had been completed and that no documents remained.

JUNE 8, 2022

The Justice Department sent a letter to Trump's lawyer requesting that the storage room be secured, and that "all of the boxes that were moved from the White House to Mar-a-Lago (along with any other items in that room) be preserved in that room in their current condition until farther notice."

AUG. 5, 2022

The Justice Department filed an application for a search and seizure warrant of Mar-a-Lago, citing "probable cause" that additional presidential records and records containing classified information remained in various parts of the club.

"There is also probable cause to believe that evidence of obstruction" would be found, read the heavily-redacted copy of the affidavit laying out the FBI's rationale for the search.

The Justice Department also revealed in the Aug. 30 filing that it had found evidence "that government records were likely concealed and removed from the Storage Room and that efforts were likely taken to obstruct the government's investigation."

U.S. Magistrate Judge Bruce Reinhart in South Florida approved the application that same day.

AUG. 8, 2022

The FBI executed the search at Mar-a-Lago, seizing 36 items of evidence, including boxes and containers holding more than 100 classified records, an order pardoning Trump ally Roger Stone and information about the "President of France."

Agents found classified documents both in the storage room as well as in the former president's office — including three classified documents found not in boxes, but in office desks.

They included items so sensitive that, "In some instances, even the FBI counterintelligence personnel and DOJ attorneys conducting the review required additional clearances before they were permitted to review certain documents."

"That the FBI, in a matter of hours, recovered twice as many documents with classification markings as the 'diligent search' that the former President's counsel and other representatives had weeks to perform calls into serious question the representations made in the June 3 certification and casts doubt on the extent of cooperation in this matter," the Justice Department wrote.

Trump and his allies, meanwhile, cast the search as a weaponization of the criminal justice system aimed at damaging him politically as he prepares for another potential White House run.

AUG. 12, 2022

Judge Reinhart unsealed the warrant that authorized the FBI to search Mar-a-Lago, which details that federal agents were investigating potential violations of three federal laws, including the Espionage Act.

AUG. 26, 2022

A highly redacted version of the affidavit laying out the FBI's rationale for searching Mar-a-Lago was released.

AUG. 30, 2022

The Justice Department responded to Trump's request for a special master in a filing that included new details about the investigation, including an assertion that classified documents were "likely concealed and removed" from a storage room at Mar-a-Lago as part of an effort to obstruct the probe.

It included a photograph of some the material found at the club, including cover pages of paperclip-bound documents — some marked as "TOP SECRET//SCI" with bright yellow borders and one marked as "SECRET//SCI" with a rust-colored border — splayed out on a carpet at Mar-a-Lago.

"Terrible the way the FBI, during the Raid of Mar-a-Lago, threw documents haphazardly all over the floor (perhaps pretending it was me that did it!), and then started taking pictures of them for the public to see," Trump responded. "Thought they wanted them kept Secret?"

___

Colvin reported from New York.

___

More on Donald Trump-related investigations: https://apnews.com/hub/donald-trump