The investigation into the riots that flared in Lozells a year ago will continue for "as long as it takes" a senior police officer said.

A total of 271 offences occurred on the night of October 22 and 23 in north-west Birmingham, launching West Midlands Police's largest ever investigation.

The disturbances left two people dead, a policeman with a gunshot wound in his leg, and hundreds of victims of assault and criminal damage.

The huge amount of evidence being collated by officers is continually increasing, but currently stands at more than 2,000 statements, 2,400 exhibits, and 4,000 tapes and discs of CCTV evidence which contains 5,000 hours of footage.

A team of 71 officers who have been working on the case recently went out to the hundreds of victims of the disorder to reassure them that work was being carried out to bring the offenders to account.

Detective Chief Inspector Una Cook, who is leading the operation, said: "It has been more complicated than any murder I have been involved with and it will take time.

"But we are committed to bringing the offenders to justice. We will continue for as long as it takes.

"We have had to buy new video equipment to enable us to look at all the evidence."

DCI Cook admitted that only a "low" number of the 271 people who were arrested have been convicted of offences since the riots.

But the officers said further investigations would see more people being charged.

Superintendent Tom Coughlan said: "There was hundreds of people on the street but it is quite obvious that there was only a small minority of people who were causing crimes.

"We had offences ranging from attempted murder to racially aggravated criminal damage.

"In the last few days our investigating team have been in and around the community talking to all the people who were affected by the disturbances."

However, there is one aspect of the investigation that finished soon after the disorder died down - that which looked into the trigger which caused the riots.

The rumour that a gang of Asian men raped a young African girl spread through the community like wildfire.

After it was mentioned on a pirate radio station, demonstrations were held outside the row of shops on the Lozells Road where it was alleged to have taken place, before the situation reached breaking point on the late afternoon of October 22.

At about 5.45pm, trouble flared outside a meeting at the New Testament Church of God, which was attended by two senior police officers and the MP for Perry Barr, Khalid Mahmood.

The incident brought others out on the street; some curious about what was happening on their doorstep, others intent on causing violence and destruction.

However, the initial allegation that a girl had been raped has not been investigated further.

But police learnt lessons about the danger of unsubstantiated rumours allowed to spread.

Supt Coughlan said: "We can go no further with an investigation into the alleged rape unless the victim comes forward. But we understand how important it us to act when a rumour spreads. We have done lots of work since on building community trust.

"I am pretty confident that if the same trigger happened now, we would not get the same reaction."