So never admit that you know anything.
Being knowledgeable about a case will get you removed.
Ignorance of what is going on will get you enpaneled in most cases.
Then the court will make sure the jury is totally ignorant of the defendants background. If you are siting on an armed robbery case and the defendant has been convicted 3 previous times for armed robbery, you will not know about it until you have reached a verdict. That works well for the guilty but not for the citizen on trial who has no criminal record.- Tom