The court on Saturday handed other defendants a variety of jail terms up to life in prison.
Former prosecutor Hisham Barakat was killed in a auto bombing in Cairo on June 29, 2015.
The interior ministry statement said security forces raided a hideout in Fayoum being used by the group, leading to a firefight that killed two members responsible for carrying out recent attacks.
The death sentences have already been approved by the mufti, Egypt's official interpreter of Islamic law, whose opinion is legally required, but not binding.
Overall, 67 people were involved in the organization of the assassination of the official, who was responsible for the investigation of high-profile criminal cases on prison escapes, where one of the defendants was former Islamist President Mohamed Morsi.
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The sentences, confirmed by the court in Saturday's hearing after the Grand Mufti's approval, can be appealed.
Hasm have claimed responsibility for a number of attacks on Egyptian security personnel in recent months, many targeting police checkpoints.
The Sinai Peninsula has been under a state of emergency since October 2014, after a deadly terrorist attack left 33 Egyptian soldiers dead.
A policeman secures the site of a auto bomb attack on the convoy of Egyptian public prosecutor Hisham Barakat near his house at Heliopolis district in Cairo in 2015.
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