Is it legal to come to a persons home or job and question about a crime committed the only source someone gave your name and told you'll go to court

They pulled him in a room in front of coworkers and my husband was told that they were investigating the murder and have only talked to two people whom are also family and one which is incarcerated led them to him. When he tells them he knows nothing about the murder which happened in another city he was told that he better find out why this certain person gave his name and call them if not they will be back and showed him a paper with a court date already set and stated that he would be going to court on that day to testify and if found that he lied he would be charged.