The New York City terrorism suspect says he was inspired by ISIS. ISIS hasn't returned the love.

When he allegedly drove his rented truck into a crowd on a bike path in lower Manhattan on Tuesday, killing eight people but aiming for more, Sayfullo Saipov had a handwritten note in Arabic in the truck. "The gist of the note was the Islamic State would endure forever," John Miller, the deputy NYPD commissioner for intelligence and counterterrorism, said Wednesday. A criminal complaint said that Saipov told investigators he had considered placing an ISIS flag on the truck, too, and asked that such a flag be hung in his hospital room. Saipov also told investigators "he felt good about what he had done," the complaint says, and many of the 90 videos on his phone are ISIS propaganda.

Yet as of early Thursday, ISIS had not claimed responsibility for Saipov's attack.

That may seem strange, given that claiming responsibility for "the worst terrorist attack in the city since Sept. 11, 2001, might be expected to project an image of strength for the group" at a time when it has lost 90 percent of its territory, says Rukmini Callimachi at The New York Times. But "with few exceptions, the Islamic State has not claimed attacks when a surviving recruit falls into the hands of the authorities." Callimachi points to ISIS-linked terrorist attacks in Brussels, Paris, Stockholm, and Canada where ISIS did not claim credit. "The constant in each of these cases is that the perpetrator was apprehended," she says.

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There are two main theories for this silence when captured. One is that ISIS is protecting its adherents from being legally tied to the terrorist organization when they face prosecution. The other is that ISIS urges recruits to die after their attacks, preferably in a gunfight with police. If the "martyrdom operation" doesn't end in death, says Jean-Charles Brisard, director of the Center for the Analysis of Terrorism in Paris, the mission is incomplete. You can read more at The New York Times.