Sometimes you're not allowed to mention the dinosaur in the room. But a throwaway reference gives the game away. 

Two recent incidents of extreme violence in London caught my eye. One was the murder of Harry Potter actor Robert Knox last year, brutally knifed by 21-year-old Karl Bishop. The court was told that Bishop carried "knives like others carry pens in pockets". 

The circumstances of the murder were horrific enough. But Bishop's attitude after the killing was equally horrendous. Told that Knox had died from wounds he had inflicted, Bishop remarked: "Yeah, sweet." He also told police to take him straight to Belmarsh prison. "I’m going down anyway. I don’t mind. I get gym every day, meals, just take me there."

Thankfully, this monster will have 20 years to enjoy prison although, personally, I'd much rather have seen him hanged.

The second case centres on 16-year-old Jimmy Mizen who was murdered when he went out to buy a lottery ticket with his older brother. The pair stopped at a bakery to have something to eat. While there they had the misfortune to bump into Jake Fahri, then 18, who had been cautioned by police several years earlier for harassing Jimmy. Fahri brushed past the brothers and the trio became involved in a scuffle. Fahri, a school dropout, attacked them with an advertising sign before hurling a glass dish at Jimmy. It smashed into his neck, severing his jugular vein. Jimmy died in his brother's arms.

Something else struck me about both stories. Either before or after perpetrating these appalling acts of violence both Duncan and Fahri grinned. Here are the exact quotes. This is from The Guardian. "During the fatal incident, Bishop walked up to Dean Saunders, 23 (another of Duncan's victims) with an evil grin on his face and stabbed him in the neck, leaving him with permanent spinal damage".

And, according to the Daily Mirror, in the Mizen murder, the court heard that Fahri fled "grinning and swaggering" after tangling with Jimmy and his older brother.

Needless to say - and this is another crucial point - both attackers smoked cannabis, supposedly a harmless drug.

All the papers covered the murder of Mizen. But few of them mentioned a little snippet of information I saw on the BBC website, contrasting the backgrounds of the boys. "While Jimmy played rugby and did well at his Catholic comprehensive school, Fahri was styling himself as a gangsta rapper, and went by the street name Dirrty Detz."

We all laughed at the Ali G character on his comedy show and his movie. Sacha Baron Cohen rarely gives interviews and he doesn't explain his characters. But those of who found him funny did so because we knew the truth of the character depicted. Urban kids with violent tendencies, trapped in a drug-induced haze of unemployment and petty crime, know they will achieve nothing the conventional way. They have no desire to work, let alone any academic qualifications or business acumen. But young men have to be the best at something. And often that's intimidation and crime. Rap music, with its glorification of guns, violence and drugs and demeaning treatment of women, is something street kids on the fast road to Loserville can relate to. Being a 'gangsta rappa' gives them street cred and a feeling of power. 

Needless to say, rap lyrics express nothing about guilt. Violence is normal and contrition seen as weakness. Hence many street kids revel in this. They need not be black - part of the joke of Ali G was that a white kid dresses up as a black kid and adopts the manner of speaking of his idols. But the role model is clear. Rappers like Snoop Dogg didn't make their fortunes through music alone. The music went hand in hand with violence or the threat of violence. And that nihilism is something that angry kids, black and white, can relate to. Perhaps everyone involved in the rap music industry, singers as well as music producers, should reflect on that.

Meanwhile, I hope that Bishop and Fahri share the same cell. And the prison officers leave them alone.