Judge Mohammed Faheem, who issued the ruling, also handed out one-year suspended sentences to two other policemen.
Ten policemen were acquitted in the same case, involving the deaths of five protesters during bloody clashes on January 28 and 29 of last year.
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It is the highest sentence handed down to policemen for their involvement in the deaths of protesters during the 2011 uprising, after previous courts issued acquittals and light sentences in similar cases.
Known as the "Friday of Rage", January 28, 2011, Mubarak's security forces fired on protesters who battled for hours until the security forces collapsed and the demonstrators conquered Tahrir Square in the centre of Egypt's capital.
Mubarak, his interior minister Habib al-Adly and six security chiefs are on trial for their role in the hundreds of killings during the uprising.
Their verdict is expected on June 2.
