Egypt’s Interior Ministry said security forces arrested one of the extremists who threw an Egyptian teenager off a ledge on top of a roof and beat him to death.
In a statement, the ministry said that security forces in Alexandria identified one of the men as Mahmoud Hasan Ramadan, and arrested him as he was hiding in a residential area in Baltim region.
The statement added that security forces were exerting efforts in a bid to arrest the other extremists who committed the crime.
Earlier on Saturday, a video posted on social media websites showed an extremist mob threw an Egyptian teenager off a ledge on top of a roof and beat him to death.
The young man who was killed, identified as Hamada Badr, 19, and his three friends were caught on camera hiding from a large group who had chased them onto a terrace in Alexandria.
The video, apparently filmed with a mobile phone camera from across the road, show the four teenagers escaping onto a 20ft ledge during violent protests on Friday.
As the teenagers huddle on top of the 20ft ledge, the mob begin throwing rocks at them and attempt to climb after them.
One bearded thug is seen carrying a black and white Al Qaeda flag.
Shortly after, three of the boys are thrown off the fifth-floor ledge and beaten as they lie on the ground.
Badr, died while his two friends were left seriously injured.
His father, Mohammed Badr, said: ‘Do you know the teenager that they killed and disfigured his body and threw from the fifth floor is only 19 and four days?
‘All he was guilty of was that he was on the roof of the building, celebrating the ousting of (overthrown president Mohammad) Mursi,” the teenager’s father added.