Ofcom has launched an investigation into the broadcasting of graphic footage from the scene of the murder of soldier Lee Rigby after receiving more than 700 complaints from viewers.
BBC News, 5 News, ITV News, Channel 4 News and Sky News are among the broadcasters being investigated for showing the pre-watershed images.
The footage showed a man holding a knife in his blood-covered hands, with a body on the ground behind.
Drummer Lee Rigby was hacked to death in Woolwich on 22 May.
Ofcom received more than 700 complaints about the footage, showing one of alleged assailants attempting to justify his actions, which was filmed by a bystander on a mobile phone.
About half of the complaints were made against ITV News, which was the first to broadcast the footage on its 6.30pm bulletin on 22 May.
The regulator is looking into whether the broadcasters breached rules which state that children must be protected by appropriate scheduling from unsuitable material, shown before the 9pm watershed.
Broadcasters who use material which may cause offence have to demonstrate that it is justified by the context.
They must consider “the effect of the material on viewers or listeners who may come across it unawares”.
ITV News defended the decision to air the footage, which was preceded by a warning to viewers. A spokesman said: “It was editorially justified to show such footage in the aftermath of such a shocking attack.”
The broadcaster said it was in the “public interest” to screen the material since it was “integral to understanding the horrific incident”.
The BBC received just over 100 complaints over its use of the footage during various bulletins.
Ofcom has no jurisdiction over newspapers, which published graphic images of the attack on their front pages and websites.