A court in Cairo has convicted four Egyptian policemen over the deaths of 37 Islamist detainees last August.
Deputy chief of Heliopolis police station Lt Col Amr Farouk was sentenced to 10 years in prison for involuntary manslaughter and extreme negligence.
The other three officers were given one-year suspended sentences.
The detainees died as a result of asphyxiation when tear gas was fired into the back of a vehicle transporting 45 of them to a prison outside Cairo.
Security officials initially said the detainees had rioted and captured a guard while en route to Abu Zabal prison on 18 August, causing the officers to respond by firing tear gas into the vehicle.
However, prosecutors found no evidence to support the claim and that the vehicle transporting them was designed to carry only 24 detainees.
Crowd-control experts said at the time that the detainees would have died in agony, gasping for air and incapable of resisting the guards.
The BBC's Orla Guerin, who was outside the court at the Cairo Police Academy on Tuesday, says there was an angry and emotional reaction to the verdict from relatives of some of the dead.
One weeping father said he was concerned that the 10-year sentence handed down to Col Farouk might be reduced on appeal.
He said his son was an innocent man who had died a terrible death, and that he and his wife had effectively died with him.
Human rights campaigners say Egypt's police operate in a climate of immunity and are rarely punished for abuses, our correspondent adds.
The deaths sparked international condemnation, with UN Secretary General Ban Ki-moon saying he was "deeply disturbed" by the events.
They took place four days after almost 1,000 people were killed when security forces cleared two sit-ins in Cairo by supporters of President Mohammed Morsi, who was ousted by the military in July.
Thousands of Islamists have since been detained, among them Mr Morsi and other senior leaders of the Muslim Brotherhood movement, who are being tried on a variety of charges including inciting murder and conspiring with foreign organisations to spread chaos throughout Egypt.