The Sheriff's department had been looking for surveillance footage -- from Bieber's cameras -- that might have incriminated him. They did not find any.
Alternatively, they had hoped that a search for text messages would show a few from Bieber bragging about his egging. Again, they did not find any evidence that Bieber "brag texted."
The Sheriff's department will send the case over to the Los Angeles County District Attorney for review this week. Without additional evidence, the case rests on the eyewitness accounts of Bieber's neighbor and his 13-year-old daughter, as well as the neighbor's video.
However, in the video, you cannot see Bieber. You can hear a voice that sounds remarkably like him, but whether or not the D.A. will believe that is strong enough evidence remains to be seen.
The D.A. decided to drop the case altogether. Or, he could charge Bieber with misdemeanor vandalism. It's possible, because of the amount of damage to the neighbor's house, that the D.A. could even go for felony vandalism.
The alleged egging took place weeks ago, long before Justin's latest legal FUBAR: his arrest over drag racing, driving without a valid license, resisting arrest, etc.