All that matters is that the finder of the phone did not take reasonable steps to return it to the true owner. From Gizmodo's own reports (and they should be presumed to not present untrue facts which expose themselves to liability) the finder only attempted to contact AppleCare, and did not take any other of the perhaps dozen more effective ways to reunite the phone with its owner. He left the bar without informing the bar's management that he found a lost valuable, nor did he leave his contact information, so that when the owner contacted the bar, repeatedly and frantically, no one could help him. Instead, he simply sold something that he knew certainly didn't belong to him for $5,000. This makes the finder a thief under California law, and since Gizmodo also admits knowing these facts, it makes Gizmodo guilty of receiving stolen goods, another crime.
Gizmodo published the name of the Apple employee who lost the phone, exposing him to public ridicule, but concealed the name of the thief who could give testimony proving Gizmodo's guilt. It is altogether fitting that law enforcement should take those steps to acquire evidence of the identity of the seller of the phone to Gizmodo.
Whether this phone was a 2007 version of the iPhone or a gold-plated diamond encrusted prototype Steve Jobs autographed model next-generation iPhone, the law is the same---the phone is valuable property, not intentionally discarded, and it does not belong to the finder. If he does anything with or to that phone besides trying to find the person who lost it, he is a thief.
There was no need to wait before gathering the evidence required to conduct a full, thorough and fair investigation, and if the evidence supports a conviction against anyone, that person should be prosecuted and punished.
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