Just my humble thoughts:

I am disturbed by this letter of the 31. It did not bother to show any concern for the victims of the crime, but is full of sympathy for the suspect. I understand that they know Xiao personally and maybe do not believe he is capable of ... (the usual blah blah), but at the minimum they should have expressed some outrage at the alleged crime, instead of simply suggesting that he is innocent just because he is such a scientific genius and valuable asset.

May I suggest that the two Mr. Fangs write a joint letter to these people (deliver in paper if necessary). No criticism or denunciation, but just some facts and a few gentle reminder. I am not sure if all of the 31 have the basic facts right. Mr. Xiao may have gotten their blind trust. Explain to them that Dr. Fang is an US educated biologist and hence also intelligent and deserving some human rights from these 31 doctors' point of view (in the actual letter don't be sarcastic like this). He has become an activist exposing corruption in China, especially those who abuse the public's trust in their professional title for personal gains. The other Mr. Fang is a journalist (hence also deserving human rights according to the prevailing value of the countries of residence of the group of 31) who risked his own life working with the good Dr. Fang in his crusade. They have been publicly threatened by Dr. Xiao in numerous occasions.... (fill in more facts; I haven't followed all the developments.)

Explain to them that while legally a person is innocent unless proven guilty beyond reasonable doubt (it is the law even in China now), as victims the two Fangs (:)) do have pretty good idea who is behind the attack. And even though every country's criminal justice system has room for improvement (some may have bigger room than others), it serves no moral purpose trying to influence the outcome of a judicial proceeding in favor of the guy you know without regard for the facts.

Also remind them of two basic principles: "Equal Justice Under Law", and "Primum non nocere." A doctor who wants to hurt and harm people is a not healer but a killer.

Make sure the letter is written in good english and must not be nasty in tone. Get people to proofread. (sorry I can't.)

Don't wage a war of nasty words against too many people. It would be a waste of time and effort and other things. Do give them the facts. Concentrate on Mr. Xiao. It is his case. If he has other partner in his corrupt doings, the facts will eventually come out.