Why did Obama pretend not to know?

Newsweek on the Benghazi attack:

The State Department, monitoring the phone calls from the consulate’s operations center, knew virtually from the first minutes, as Ubben, Stevens, and Smith were hiding, that the attack on the consulate was no protest gone astray. And when a major CIA outpost nearby came under attack hours later, there was little doubt about that being an operation by well-trained terrorists.