Based upon your description, it would be wise for you to assert your fifth amendment right. You must still appear in court if subpoenaed, but you should let the D.A. know you will refuse to answer any questions. The D.A., however, can offer you use "immunity" - in writing - which means you can be compelled to testify - assuming it's a felony matter - but anything you say on the witness stand will not be used against you. Of course, they could still charge you with a crime for anything you said already and/or any other evidence they might have of criminal conduct on your part, if any.
There is always a chance that you could still be charged in this instance. This is specially true considering the DA comments. You have to appear to testify if you were properly served with the subpoena but I agree with the other attorney, I would plead the 5th in all aspects and not even answer questions about your presence. If you need to be there I would go with counsel.
As you have figured out, you made several mistakes here: You got involved in the wheel theft, even if not directly. You talked to the DA and apparently 'ratted out' both your friends and yourself. You talked to the DA apparently without having your own attorney present, and told the DA everything you knew about anything. And, now you think that protecting yourself by taking the Fifth Amendment looks 'strange'? No, get an attorney (hired or Public Defender or other appointed attorney since it is likely one or more of your friends already has the Public Defender representing them, and practice saying 'On the advice of my attorney, I claim the privileges of the Fifth Amendment.' Or, perhaps your attorney can get you immunity from prosecution if you agree to testify. Hope this helps.
Although I am an experienced CA criminal defense and appeals attorney, I can not 'guarantee' that my answer is entirely accurate, since I have not reviewed all of the factual circumstances of the case, nor have I discussed those circumstances fully with the questioner. The fact that I have answered this question does not establish an attorney client relationship between the questioner and my self or my office.
You are not required to show up unless you are subpoenaed. Next I agree with the others that invoking your 5th amendment may be a good idea. HOWEVER, that may not let you off the hook, because the DA could offer immunity. Regardless, you should tell the judge that you would like to speak to an attorney because you do not want to incriminate yourself. If you are offered immunity you can be forced to testify, unless you want to go to jail instead.
You need a lawyer, the court will appoint one if you cannot afford one.
The above information does not establish an attorney client relationship nor is it meant to provide legal advice.
If you are legally subpoenaed you must appear in court. However, you may have a privilege not to testify if anything you say can form a link in the chain of your guilt. It is not clear if you could be charged under an aided and abeter theory. In other words, if a person knows someone else is about to commit a crime they do not have an obligation to stop them ( there are a few exceptions) but if the person helps aids, encourages, assists,helps them get away etc then you could also be prosecuted just like the thief. From what you have described you may have some liability since ther is apparently enough for the DA to threaten you with prosecution. Nor way of dealing with this situation is for your lawyer to first determine if you have liability and second to negotiate an immunity agreement. If the DA grants you immunity you know longer have a Fifth Ammendment privilege to this activity.SJP