Rust Testimony

This is an old case that happened in the 1990s. Lin Xiaoyue, a female textile worker, was murdered in an abandoned factory. There were many exhibits at the scene, including a four-eye button. The new criminal police captain, Chen Xu, listed this case as a key research target during the retrial of old cases. Unexpectedly, an old case that was brought up again now would cause huge resistance. What is the reason for this that keeps all parties secretive?