Commentary for Kiddushin 131:15

Rava says that this is not simply a case of contradicting witnesses. The second witnesses refute the very possibility of the first witnesses knowing that Yannai’s mother was taken captive. For instance they say that the first witnesses were elsewhere when they say they saw the event. This is called “hazamah” which is a special category in which the second witnesses are believed. Thus we do not need to say that there was only one witness.