In this question, someone asked if someone told you that he committed a crime, that doesn't mean that you know it's true.
If you have knowledge of a serious crime then you can (and in some jurisdictions, are required) to report it to the police.
However, you don't have such knowledge
People say things that aren't true. They do this a lot on the internet. In fact, it was I who shot JFK: I did it 5 years before I was born which is a neat trick but not beyond the abilities of the mafia/Cuban/Russian syndicates I was working for, when they catch me I will tell them how it was done.
That's because he may lie. He may made stories up. Not just because someone told me he murdered someone means he really did.
In fact, many famous people, admit that they committed a crime. Obama admitted using ganja. Steve Jobs admitted using LSD. Why aren't they convicted? Because we don't know they really did it.
Someone told Ryan Holle they gonna rob somebody. Ryan thought it's a joke. Latter he lend his car. Why did the jury presume that Ryan knows that someone would rob a car simply because they said so? They could be joking.
Based on what I see, Ryan probably didn't know they gonna rob somebody. If he knew, he wouldn't lend the car. Why would he? Do they have agreement to split the spoils of robbery? He lend the car, not renting it. He gets nothing out of the robbery even if it's successful. Why would anyone risk long jail time lending a car if he knew there is a robbery.
Chance is he didn't know.
Why did people convict Ryan anyway?