The Big Question: Is offering immunity from prosecution the only way to solve some crimes?

Why are we asking this now?

Police investigating the murder of 11-year-old Rhys Jones in Liverpool encountered a wall of silence. For months, the investigation stalled as officers tried to persuade people to come forward to say what they knew. In the end, a 17-year-old member of the gang responsible for killing Rhys agreed to become an informant and key prosecution witness referred to in court as Boy X. The Crown Prosecution Service (CPS) was originally going to charge him with firearms offences. Instead, it offered him immunity from prosecution provided he met conditions including a requirement to attend court and give a truthful account. He accepted those terms and entered into an immunity agreement. Soon after this, the CPS decided there was sufficient evidence to charge Sean Mercer with murder.

Why don't police force witnesses to help them convict criminals?

Police officers can arrest people for obstructing their inquiries, withholding information or perverting the course of justice. But this will not necessarily help in getting a witness to testify in court. Faced with the prospect of being identified as an informant, many witnesses choose to remain silent. They know that defendants, in the course of the pre-trial process, will be told the names of witnesses giving evidence against them. Once the name is out, it may be easy for a suspect to intimidate a witness. Cases sometimes collapse after a chief witness changes their mind in mid-trial and refuses to testify. The prosecution may be convinced that the witness has been "nobbled" – but the law prevents the jury being told of their suspicions.

So what are the alternatives?

It is a principle in English law that those who turn Queen's evidence may escape prosecution or be given lenient sentences. Boy X was originally a suspect in the murder inquiry but, in a deal brokered by the police and the Crown Prosecution Service, he was granted immunity from prosecution. Witnesses who refuse to give evidence because they fear for their own safety can also benefit from promises of protection offered by the CPS. Protection schemes are run by different police forces. In extreme cases, vulnerable witnesses can be moved to new addresses and given new identities. For some this protection can last for a lifetime. In the Rhys Jones case, Boy X will start a new life away from the Liverpool suburb of Croxteth in which the convicted gang members and their families live.

Do other countriesdo the same?

America and Italy have led the way in immunity and witness protection programmes. In the US, prosecutors have relied since 1970 on the Organised Crime Control Act to help fight the Mob. The law has origins in the 1871 Civil Rights Act designed to protect people testifying against Ku Klux Klan members. In Italy, similar deals are offered to Mafia informants.

How successful is this in practice in Britain?

Cases in which witnesses are given protection often end in convictions. Juries tend to be impressed by people who perform a public duty in the face of threats to their safety and so give their evidence due weight. But a recent House of Lords ruling made it clear that the practice of offering anonymity to witnesses had become far too widespread and deprived defendants of their right to know who their accusers were. The police and CPS have had to revise the offer of anonymity in the light of this ruling.

Who has previously taken part in the scheme?

Danielle Cable has been a protected witness since 1998, when she helped to identity a known underworld boss, Kenneth Noye, as the man responsible for stabbing to death her boyfriend, Stephen Cameron, in a road-rage incident on the M25 at Swanley, Kent. In a rare interview about her life, she told how she had had to virtually cease communicating with her family and friends. "I have lost twice – Stephen and my old life," she said. She added that she feared becoming the victim of a contract killing one day. The witness programme was also used in the case of Jamie Robe, 17, who was murdered on the Osprey estate in Rotherhithe, south-east London, in 1997. Twenty people – witnesses and their families – were moved out of the area. Yet witness protection does not have a 100 per cent record. In 1999, the IRA "supergrass" Martin McGartland survived an attempt on his life when he was shot six times in the stomach. Boy X may have to spend the rest of his life looking over his shoulder.

Who was the most famous grass?

That dubious honour must go to Britain's first supergrass, Bertie Smalls. Swapping a career as a successful bank robber for an immunity deal under which he shopped dozens of his colleagues in 1974, he escaped jail and kept whatever cash he had not spent on drink, gambling and women. On Smalls's evidence, 27 men were jailed for a total of 322 years. His immunity agreement was criticised by Lord Justice Lawton, who demanded that no Director of Public Prosecutions should ever enter into such a deal again. Smalls's actions encouraged a flood of other surpergrasses to "do a Bertie". He died of natural causes earlier this year.

How has the law changed?

Under the Serious Organised Crime and Police Act 2005, prosecutors can serve a written notice on a criminal either giving complete immunity from prosecution, immunity if he complies with certain conditions, or an undertaking not to use particular evidence against him. This formalises the practice which operated before the Act. Boy X is believed to be one of the first to benefit from new guarantees of immunity from prosecution.

Can these measures alone bring about successful prosecutions?

Offers of immunity from prosecution and a place on a witness protection scheme can break down walls of silence by flushing out key witnesses. But a single testimony from someone who may have been a suspect until the offer of an immunity deal must be supported by other evidence. Without such evidential safeguards, the system is open to abuse, because a criminal wishing to save their own neck might be tempted to say whatever the police wish them to say.

Who else can help solve these crimes?

Some sections of society have always been suspicious of the police. This is especially true among ethnic minorities and parts of Northern Ireland. To combat this reluctance to help officers investigate crime, successive governments have placed great faith in community policing. By making visible contact with inner-city areas and other problem districts, police gain the confidence of the community. But distrust of the authorities remains an intractable problem, especially where generations of families have had to live as outsiders without regular work. Loyalty to the family and the community come before the interests of the state. The most effective way to break down this hostility is through proper investment in urban regeneration and the creation of more jobs.

Are immunity deals a necessary tool for police officers today?

Yes...

* When police have no other evidence, immunity deals may be the only way to get a case to court.

* They have worked to bring successful prosecutions against members of the Mafia.

* Where a community is living in fear of a crime, immunity deals for gangs can break the wall of silence.

No...

* Old-fashioned detective work can solve crimes without giving immunity to those who should be put on trial.

* Immunity and anonymity deals can lead to miscarriages of justice.

* Social reform programmes tackling poverty can end the public distrust of the police and lead to better co-operation with the authorities.