There were 50 teenage murders across the UK in 2007, 16 already this year in London alone, but often no-one comes forward.
In 2005, 73 teens were prosecuted for having a knife at school
1Xtra News has been trying to find out why so many young people refuse to go to the police when they witness a crime.
Six years ago, Erica's brother was murdered in Manchester in a drive-by shooting and police still don't know who shot him.
She said: "I arrived at the scene. I could see what appeared to be a body on the floor because there was obviously lots of blood.
"But it was covered over. But I was told by police that that was my brother."
Erica says she couldn't believe it was her brother who'd been killed.
She said: "I think it was not until I went to the morgue and actually saw him.
"I thought he was going to get up and start laughing.
"It was when I bent down and went to give him a kiss and then I could smell he was dead and feel he was dead."
He was killed on a busy street in Manchester but no witnesses came forward.
Erica added: "A lot of young people possibly might have been present or knew that the friend had shot somebody.
"The police are like the opposing gang, aren't they? So it's totally disloyal to actually speak out. So they don't want to do that."
A lot of teenagers agree.
One teenager, who didn't want to be named, said: "The police are the first people to say, right, that was him that told me you know, straight.
"I wouldn't tell police if I saw someone get stabbed in the street. I'd walk past it."
Police say they're trying to build bridges and things are getting better.
In court, witnesses can give their evidence from behind a screen and with their voices disguised, like 14-year-old Luke.
"At first I said, 'No way am I going to court. I'm too afraid.' It took just over a year to go to court.
"I don't have to look them in the eye and didn't even have to see them."
US-style witness protection programmes are becoming more common and in some cases names are changed before people give evidence.
Teenagers in Manchester say they don't come forward because they often know the person who's carried out the crime and fear they won't be protected by the authorities.
One unnamed youngster said: "OK. You've witnessed something that's happened in the community but do you come forward?
"It comes to the point where you've got to draw the line between what's right and what's wrong."
Teenagers say they don't come forward because of a lack of trust
Another teenager's mate was seriously injured after a fight over where she lived.
She said: "There were, like, 10 girls. Something happened between one of their friends and her friends.
"So they decided, in revenge, to beat up the girl. She's from a different area so that's why they didn't get along.
"She had to go into hospital because someone broke one of her bones somewhere.
"She was really badly hurt, bleeding and all sorts. I just thought to myself, 'How can people do this.'"