If I found out a relative stole merchandise from a store 3+ weeks ago, can i still turn them in?
Yes, you can turn the person in by calling the police. However, there is no way to know if a prosecuting attorney would then choose to pursue this case. A shoplifting charge could be hard for a prosecutor to prove after-the-fact (like without eyewitnesses or store video). Also, you should ask yourself if you are truly prepared to burn the bridge with this particular relative. The ramifications of a criminal charge can be very, very long-lasting and this person is going to find out that it was you who turned him/her in to the police.