One of the hardest things for someone who has a legal case is to refrain from talking in detail about the alleged offense. It's tempting to assume your criminal defense attorney would benefit from knowing everything. However, there are several reasons why you shouldn't confess everything to counsel.
Your Lawyer Probably Doesn't Need Those Details
To the extent a criminal defense attorney needs to know something, they will ask you for the information. Remember that it's not your lawyer's job to get to the bottom of anything. That's the prosecution's problem. Your attorney is simply trying to explain to a judge or jury why the prosecution hasn't met its burden of proof. A lawyer rarely accomplishes this by digging into details and discovering something that happened.
When the time comes that an attorney needs to know the details, they'll let you know. For example, your criminal defense lawyer might reach a cooperation agreement with the prosecution that offers immunity. Generally, that situation requires you to confess everything you know to execute the agreement. In that scenario, failing to disclose anything may leave you open to later prosecution. However, that sort of deal is a low-probability outcome for specific cases.
The Truth May Limit Your Defense Options
A criminal defense lawyer can't tell a court anything they know to not be true. Suppose a defendant wants to assert that they were in a different state at the time an offense occurred. The attorney can only present that defense as long as they don't know for sure that it's false. If the defendant tells the lawyer that they were in town on the night of an incident, they can't subsequently tell a judge or jury that the defendant was out of the state.
There are extreme versions of this scenario where the lawyer may have to leave the case or even become a defendant themselves. No one wins in that scenario. The best the defendant can hope for once a contradictory truth is out there is getting a new lawyer without the old one facing sanctions or prosecution.
You Might Not Be So Guilty
Legal guilt is a distinct thing from whatever personal sense of responsibility you might have for an alleged offense. It's not wise to presume your guilt based on how you feel or even what you saw. Let your criminal defense attorney do their job. Don't do the prosecution's job for them.