According to the friend’s account to the police, Mr. Abaaoud regaled them with stories about how he had made it to Europe by inserting himself in the stream of migrants fleeing across the Mediterranean. He explained that he was among 90 terrorists who had made it back and who had gone to ground in the French countryside, the friend told the police.

“Abaaoud clearly presented himself as the commander of these 90 kamikazes-in-waiting, and that he had come directly to France in order to avoid the failures they had experienced in the past,” the police said the friend had told them.

Mr. Abaaoud would spend four days and three nights camped in the bushes, while his cousin returned with cake and water. By the friend’s account, Mr. Abaaoud told Ms. Aitboulahcen that he and an associate would carry out further attacks. Ms. Aitboulahcen was sent to buy the men new suits and dress shoes, the report said, bought with the nearly 5,000 euros the Islamic State’s network had sent via Western Union and an informal money exchange network known as a hawala.

On the night of Nov. 17, Ms. Aitboulahcen secured an apartment in the Saint-Denis suburb of Paris, chosen because the landlord did not require receipts.

The police raided it early the next morning, with Mr. Abaaoud and his cousin inside. The thundering boom of an explosive vest was recorded by television news crews outside.

Inside, the police again found the components used to make the TATP bombs. In addition to other weapons, they found a Herstal pistol with an empty clip, smeared with Mr. Abaaoud’s DNA, suggesting that he had fought to the end.

His body was found on the building’s third floor, and mixed in with his flesh were ball bearings and fragments of plastic. His feet were still in the orange sneakers.

Inside the ruins, the police found several dozen boxes of unused cellphones still in their wrappers. The phones were found throughout the rubble, including in the rooms and stairwell. Others had been ejected during the blast and fell onto the street below.