What the defendant says to his lawyer is confidential. The lawyer telling someone else what his client said in confidence is grounds for the lawyer's disbarment. If someone testifies that 'I was told that so-and-so did such-and-such', that isn't evidence; it's called hearsay - the testimony would not be based on one's own personal observations and recollections.Maybe you need to describe it better then. The only person that the defendant talks to is his lawyer and that's in private. He gives the lawyer the details of the alibi in private. The lawyer then takes if from there. Not sure what the problem is.
Nothing prevents an accused from speaking out on his own behalf in Court, but there are limits to the amount of help his lawyer can do for him if a defendant takes the witness stand. The phrase 'everything you say can and will be used against you' applies in Court, as well as in a police barn.
Saying nothing at all ensures that nothing that one says can or will be used against them, unless a deaf mute takes the witness stand, and testifies in sign language.
Often a defense attorney doesn't want his client to tell him their version of events. If the client tells the lawyer that he did the deed, but wants to try to get away with it, a few lawyers will excuse themselves from the case out of moral principles, and many will raise their fee.
The defense lawyer is not necessarily trying to convince the Judge and jury that his client is not guilty. Usually the defense is looking to try to have prosecution evidence excluded because of procedural errors in the evidence gathering, or to cast doubt on the accuracy of an eyewitness' memory recall, or to present a plausible explanation of how the crime may have been committed by someone else. In a nutshell, the defense is often trying to create reasonable doubt,and nothing more.
In a case based mostly on circumstantial evidence, a degree of doubt should exist in the minds of the jurors. The jury's job is NOT to decide whether or not they THINK the defendant is guilty. Their job is to decide whether or not the prosecution has PROVEN the guilt, reasonably and sufficiently.
There is no place for emotion in rendering a verdict. No one should ever be convicted because the jury 'feels that they probably did it'. Lawyers will try to provoke emotional reactions from juries to cloud their judgement. Part of the job of the jury is to see through that sort of thing. Evidence, as defined by the Law, is the ONLY thing that matters in a criminal trial.The rest is theater.