Protesters who held extremist placards during a protest over cartoons of the Prophet Muhammad could be charged with incitement to murder, police say.
Police made no arrests on the day of the protest
Some placards at the protest outside the Danish embassy in London threatened a repeat of the 7 July bombings.
The Met Police are studying more than 60 hours video of the 4 February demo.
Assistant Commissioner Steve House said the Crown Prosecution Service would decide what charges, possibly including incitement to murder, were brought.
"The type of offences we are looking at are public order offences and we are looking at incitement to violence," he said.
"Some of the placards talked about killing. It may be incitement to murder - that is what the Crown Prosecution Service [decide] and that is why we are going to be sending a file to the CPS."
The Met Police are warning demonstrators not to parade offensive placards at a further planned rally in London on Saturday.
No protesters were arrested during demonstrations last Friday and Saturday over the cartoons first printed in a Danish newspaper, but specialist police officers took film and photographic evidence.
Scotland Yard has received 500 complaints from members of the public about the protests.
Earlier this week, Downing Street said police would have "our full support" in any actions taken.
"We believe some of it was unacceptable but it's up to the police to decide whether to prosecute," Prime Minister Tony Blair's official spokesman said.
A demonstrator who imitated a suicide bomber in the protests has been recalled to prison.
Omar Khayam, 22, of Bedford, is a convicted drug dealer who was jailed in 2002 and released on licence last year after serving half his sentence.
He was arrested and recalled to prison for breaching the terms of his licence.
Khayam apologised for his "insensitive" protest on Monday but said he had been offended by the cartoons.
Over the weekend mobs in Syria and Lebanon torched the Danish embassies in Damascus and Beirut.
Among the cartoons which have sparked outcry among Muslims is one of Muhammad with a bomb-shaped turban on his head. Newspapers in Spain, Italy, Germany and France reprinted the material.