The police arrested 14 people on Monday on charges of involvement in the violent clashes that have been taking place in Port Said over the past few days.
One of the detainees was reportedly videoed shooting dead two policemen.
The man, according to Al-Ahram's Arabic website, appears in footage gunning down Lieutenant Ahmed El-Balki along with a low-ranking policeman, both of whom died in the early hours of the attack on the coastal city's prison on Saturday.
Those who were arrested reportedly had in their possession four automatic weapons, 10 pump-action shotguns, and live ammunition.
A court on Saturday sentenced 21 Port Said residents to death for their involvement in last February's Port Said stadium disaster, in which scores of football fans were killed.
Since then, the city has witnessed intense rioting, with residents accusing the central government of scapegoating and marginalising them.
The clashes followed earlier confrontations across the nation on Friday, the second anniversary on of the January 25 Revolution.