Former Trump campaign chairman Paul Manafort agreed to testify, out of the public eye, before a group of congressional staffers on July 25. Whatever he said that day, it apparently didn’t satisfy Special Counsel Robert Mueller and investigators at the FBI. Not only did they conduct an early morning raid on Manafort’s Virginia home the next day, that raid was more intense than earlier stories may have suggested.

According to a source familiar with the investigation, Manafort was awoken by a group of armed FBI agents knocking on his bedroom door as they executed the warrant on July 26.

Notice that agents weren’t knocking on Manafort’s front door, but his bedroom door. That means that agents likely entered the house on a no-knock warrant. These are warrants that are often used in drug cases where there’s a concern that an announcement of police at the door may be followed by the sound of a flushing toilet, but they’re also used in related cases—cases where there’s a strong expectation that serving a warrant in a normal way could lead to destruction of evidence.

Paul Manafort has been playing the foreign agent game for decades, and over that time he’s dealt with dictators on four continents along with a series of mail-drop “offices” and numbered bank accounts. It’s entirely possible that his house was already cleaner than an operating room.

But the fact that the FBI went to his home in force, with a no-knock warrant, means that Mueller had reason to believe it might not—and that they went to a federal judge with both reasons to believe that a crime had been committed, and a contention that Trump’s campaign chief could not be trusted to hand over evidence.

A spokesperson for Manafort confirmed the warrant to ABC News and said in a statement, "FBI agents executed a search warrant at one of Mr. Manafort's residences. Mr. Manafort has consistently cooperated with law enforcement and other serious inquiries and did so on this occasion as well."

Cooperating with armed FBI agents who appear at your bedroom door is generally considered a good idea.