Perhaps this case was difficult because one of her witnesses was either a relative or another invalid witness. We are reminded that Rabbi Akiva sates that two witnesses are always enough. A third is used only to be stringent. If two witnesses were disqualified, all would be punished like the first, even if the third's testimony was irrelevant/unnecessary. Does this only apply to capital cases, the rabbis wonder? And would it apply to 100 judges? We are reminded that the testimony is disqualified only if the invalid witness warned the transgressor.
But what if a person was murdered in front of two brothers who could not testify against the murderer? Again, the rabbis turn to whether or not the transgressor was warned before committing the crime. We are told that the testimony right be eliminated anyhow due to conflicting stories.
The Gemara opens up questions of monetary liability accompanying death penalties. Witnesses might be filled, too. Punishment follows attempts to kill witnesses. They also pay, because they tried to cause a loss to someone else.