If the law enforcement is trying to find a murderer, or they're trying to catch a drug lord or trying to prevent a school shooting, and they have leads and they have suspects, then it's perfectly fine for them to tap the suspect's phone, and to intercept his Internet communications.
比如如果执法机关正在寻找一名谋杀犯 或者搜捕一个贩毒者 或者试图阻止一场校园枪击案的发生 并且他们中有头目有嫌疑犯 此时如果能监听他们的手机 截获他们的网络通信那就太棒了