Good question. Somebody loyal to President Mohamed Morsi is reportedly shooting tear gas at protesters from the Presidential Palace.
On the other hand, according to unconfirmed reports from numerous Twitter users, some Egyptian riot police sympathize with the protesters.
This Tweeter says some Egyptian police took off their uniforms, left them in a heap on the ground, and joined forces with the anti-Morsi protesters:
Several Twitter users allege that police let protesters cross barbed wire as they approached the Presidential Palace:
Earlier today, smiling police were photographed shaking hands with protesters: