New laws to tackle gun and knife crime will not work, a senior police representative has said.
Paul Erhahon was stabbed to death on Friday
Alan Gordon, vice-chairman of the Police Federation, spoke after the fatal stabbing of 14-year-old Paul Erhahon on Friday.
Mr Gordon said some people had a "scant regard" for human life which would not be combated by legislation.
The Violent Crime Reduction Act introduced a range of new offences relating to gun and knife crime.
Mr Gordon said he thought the intention to try to control violent crime was good but added that he was cynical as to whether legislation was the right answer.
"People that seem to have such a scant regard for human life, I don't think are going to be dissuaded in their actions by new legislation," he said.
"It is a very difficult tightrope for the home secretary to walk - as to whether he should introduce new legislation to try and show toughness.
"But actually, how effective it is going to be is debatable."
The scene of the latest stabbing incident in London
Mr Gordon was speaking in response to the death of Paul Erhahon who collapsed yards from his home in Leytonstone, north-east London, after being attacked by a gang.
A 15-year-old he was with, whose name has not been released, also suffered stab wounds and is in a critical condition in hospital.
A 13-year-old boy and a 19-year-old man were arrested in the early hours of Saturday and remain in police custody.
The latest attack follows the killing of five other male teenagers in London in the past two months.
It sparked claims that gun and knife crime in the UK were out of control in some areas of the country.
Norman Brennan, of the Victims of Crime Trust, said: "The government must ensure that border controls are tightened up to stop the guns coming in, and we need to do targeted and random stop and search of those who carry guns and knives on the streets of Britain unopposed.
"You can make sentences for those that carry guns as high as you want but many young teenagers have no fear of life and live or die by the gun, so however high the sentence it will not deter them.
"The only way is to effectively disrupt them from carrying them by having many more armed response units and the stop-and-search must be done en masse and supported by all communities - who surely are sick and tired of living in fear of gun and knife attacks."
LONDON'S TEENAGE VICTIMS
James Andre Smartt-Ford, 16, shot in Streatham, 3 February
Michael Dosunmu, 15, shot in Peckham, 6 February
Billy Cox, 15, shot in Clapham, 14 February
Kodjo Yenga, 16, stabbed in Hammersmith, 14 March
Adam Regis, 15, stabbed in Plaistow, 17 March
Raymond Stevenson, of Urban Concepts, an anti gun and knife crime campaign group based in London, said: "We have taken our eye off the ball over the last ten years.
"Young people have been overlooked and there have been escalations in the community which no-one has really looked into - the closing down of youth facilities, the lack of investment in our young people, specially in the urban communities and black communities.
"And it was always going to reach this point. And I think it's going to get worse."
The Violent Crime Reduction Act came into force on Friday, after being rushed forward by the government in response to the spate of gun and knife deaths.
The new laws make it an offence to get someone else to carry or hide guns and knives.
Those found guilty of using children to hide firearms face a sentence of up to 10 years and those using minors to mind knives will face up to four years in prison.
People using other adults will face a maximum jail sentence of five years.
The range of offences for which an offender can be given a mandatory minimum five-year sentence was also extended beyond simple possession of a banned firearm.
The maximum sentence for carrying an offensive weapon was raised from two to four years' imprisonment last year.