If the defense doesn't want to gather any, then it doesn't have to and it certainly wouldn't be going after any potentially harmful evidence. But, getting some basic defense evidence is a lot easier than you seem to make it out to be - I'm assuming you would have an alibi for why you didn't commit a murder and I imagine you could get some evidence supporting the alibi could be fairly easy. Testimony from a friend that you were hanging out, traffic logs from a streaming service or a game service that you were at home watching/playing when the murder happened, GPS data from your phone, whatever. A lawyer could at least request if not get that in a week or two without any issue.