Before I was old enough to read its inscription I asked my mother about a small, rose quartz memorial tucked beside our local Boots chemist that seemed out of place among north London shops and restaurants. It was for PC Blakelock (pictured) the Muswell Hill bobby who died trying to protect firemen during the Broadwater Farm riots in Tottenham on 6 October 1986. He was hacked to death with machetes by a mob chanting "Kill the pig!"

It was London's first taste of Tottenham riots, and like last year's, shone a spotlight on huge economic and social inequality, as well as serious problems in the police force. Winston Silcott, Mark Braithwaite and Engin Raghip were convicted of the murder in March 1987 – only for all three convictions to be overturned on appeal. Charges against a further three juveniles were dismissed. Detectives involved in the case were tried for perjury and perverting the course of justice, but later acquitted. The investigation was a mess and the murder remained unsolved for 27 years.

So, I was fascinated to read yesterday that DNA evidence could finally bring a "realistic prospect of prosecution" against a man who was under 18 at the time of the murder. It made me think of PC Blakelock's widow and three children who have lived with the disquieting fact of prolonged injustice for nearly three decades. When it has been mired in mistakes and confusion for so long, will a new potential certainty, the face and name of one his murderers, possibly bring comfort?

I suspect the catalyst for last year's riots, the nature of Tottenham man Mark Duggan's death, will remain similarly murky in three decades. Murder is inexplicable to most of us. Knowing who committed it, even though the circumstances remain unchanged, is important because it provides the opportunity to ask the question: Why?

This was the subject of last night's Radio 4 programme The Victim's Voice, in which families spoke with the murderers of their loved ones in Brixton Prison. It showed poignantly that the answer to "Why?" is often bewildering, or worse, trivial. At school a classmate of mine was stabbed in the chest. He survived, thankfully, and we had the opportunity to ask "Why?" Bafflingly, it happened during an argument with his best friend over a packet of crisps. In We Need to Talk About Kevin, the child murderer's reply is: "I used to think I knew, but now I'm not so sure".

The answer is not always helpful. But the opportunity to ask is important. PC Blakelock was an individual a mob called "pig". They probably didn't know his name, but his uniform represented the whole police force. The discovery of their names won't solve anything. But it will be a start.

@MatildBattersby