Immediately after the incident. Not 40 days later, under massive public pressure. That's the difference between the Trayvon Martin murder case and this one.
The three aggressors have been arrested and charged with aggravated battery.
On a side note, some have noticed that this incident has been underreported by the mainstream media. It could be because the attackers in this case were black and the victim was white.
Also, it's "under-reported" because it's a typical crime. People weren't outraged about Zimmerman because the kid he murdered was black, they were outraged because police refused to prosecute until after a massive public outcry nearly 40 days later.
For all the things that I never did
For all the places I never was
For all the people I never stopped
But there was nothing I could do..."