Code comments are vital for software development and maintenance. To supplement the code comments, researchers design automatic tools for method-level comment generation. The prior tools generate comments that explain code functionalities, but cannot generate comments that explain why code was developed as it is. Issue reports contain rich information on how code was maintained. The valuable details of issue reports (e.g. maintenance types, symptoms, and purposes of modifications) are useful to understand source code, especially when programmers learn why code was developed in a specific way. To generate such comments, it is desirable if an approach can automatically build the links between code fragments and issue reports. In this paper, we propose the first approach for this research purpose. Our results show that it relinks more than 70% issue numbers that are written by programmers in code comments. Furthermore, the links built by our tool covers 4X bugs, and 10X other issues than the links written in manual comments. We present samples of our built links, and explain why our links are useful to describe the functionalities and the purpose of code.