You have written correctly: R. Alexandri may not compel the witnesses to reveal their testimony, until they appear in court to have it recorded by order of the judges. Furthermore, he may not cause the ban to be pronounced against the witnesses, if they are willing to testify without recourse to the ban. However, if R. Alexandri fears that other witnesses may withhold their testimony, he may, by the authority of the judges, compel you (the community?) to pronounce the ban against any and all witnesses who refuse to testify. SOURCES: P. 296.