The murder of Brent Martin, a 23-year-old man from Sunderland with learning disabilities who was beaten to death for a £5 bet, shocked the country. Liz Sayce, Chief Executive of the Royal Association for Disability and Rehabilitation, argues that more should be done to protect disabled people from crime

I'M not going down for a muppet." So said one of the killers of Brent Martin, a Sunderland man with learning disabilities beaten to death in a horrific attack, as quoted at his trial.

It is difficult to be sure which is more terrifying: the fact this callous teenager seems to believe there are people worth risking his freedom to murder in cold blood? Or is it that he believes that, because Brent Martin was what he called a "muppet", his life was less valuable? Was Brent Martin, like a target in a computer game, worth only half the points of a non-"muppet"?

The Criminal Justice Act now states a judge must take into account whether or not a victim's disability was an aggravating factor in an offence. If it is, the judge is obliged by law to increase the sentence.

Disability rights groups campaigned hard for this "hate crime" law - and welcome it.

Did we believe tougher sentences alone would stop crime against disabled people? Of course not.

They will not stop all, or even many crimes. But if they only save one life, they will be worthwhile.

Tougher sentences for disability hate crimes are only the visible tip of a very large iceberg of effort which needs to be made for crime against disabled people to be reduced.

Brent Martin's death, the latest in a string of incidents across the country in which people with learning disabilities have been bullied and eventually killed, has brought the issue to public attention.

But when the spotlight moves away, disabled people - especially those with learning disabilities - will continue to be at risk of intimidation, violence and exploitation.

The majority of this will never be reported, or even witnessed.

Disabled people, especially those with learning disabilities or mental health problems, face enormous obstacles in reporting crimes and getting them solved. To overcome this, three things are needed: ■ Genuine outreach and commitment to taking disability into account from police forces, the Crown Prosecution Service and the judiciary; ■ Police staff with experience of working with people with learning disabilities, and more disabled police officers; ■ Education for people with learning disabilities to ensure they know their rights and feel able to report crimes against them.

I do not know whether Brent Martin's disability was an "aggravating" factor in his murder. Only the judge, with all the evidence, can make that call.

Brent Martin's killers displayed a staggering savagery, sadism and lack of human decency. It is quite possible such youths would have killed someone - anyone - sooner or later. It seems they killed Brent Martin because they could, because they thought it was fun, and they did not need any other reason.

Perhaps they are equally contemptuous of the life of any human being, not just one with learning disabilities. Perhaps they are equal-opportunity murderers.

But one thing has been abundantly clear since the start of the case: Brent Martin's disability was a factor in his murder. For not only are his killers amoral and sadistic, they are also cowards. Of all the people they could have chosen to murder, why did they choose him?

For the very simple reason they knew he would not fight back.

Brent Martin was physically capable of defending himself, but he did not. Not for nothing has he been called "a gentle giant". As his family have said, he thought everyone was his friend. Jurors wept as they heard how he kept apologising to his attackers. It is this aspect of this heinous crime, perhaps more than any other, which has outraged public decency the world over.

A Canadian blog, Chewing the Fat, has organised a black armband campaign in Brent's memory, which has met with much success.

Brent Martin's murder has resonated with disabled people and their friends and relatives around the world because they know only too well the levels of violence, intimidation and exploitation to which disabled people are routinely exposed.

I have been a disability rights campaigner for many years. I have worked for and with many highly talented and capable disabled people. The last thing I want is to encourage others to view disabled people as victims or objects of pity. We are not - but it would be foolish to deny that people with physical disabilities, learning disabilities and mental health impairments are at greater risk from crime. Criminals do not obey the Disability Discrimination Act, and disabled people are viewed as soft targets.

Imagine a paedophile choosing a victim. There are two children, one who can report him, and one who can't, because they have learning disabilities and are unable to speak or sign. Which does he choose?

Imagine a mugger stealing wallets. He has two potential targets, one who can run away and struggle, and one who can't, because they have physical disabilities. Which does he choose?

Finally, imagine murderers choosing a victim to kill for pleasure. They have two potential targets, one who will fight back, and one who won't. Which do they choose? In the tragic case of Brent Martin, we know.

Given two victims, with equal consequences for the criminal if discovered, most criminals will choose the softer target. Why wouldn't they? This is why, in addition to tougher sentences, police engagement with disabled people and the provision of training to ensure people with learning disabilities and mental health problems are dealt with correctly and taken seriously are essential.

The successes of the disability rights movement will count for little if disabled people are too afraid to exercise their rights to social inclusion. Taking crime against disabled people seriously before, during, and after investigations will send the message that criminals should think twice before picking on a softer target. Ultimately the police, CPS and judiciary must take a victim's disability into account at all stages for one simple reason. Criminals do.