Bigamy in law refers to registering marriage with others before the marriage is dissolved;
De facto bigamy refers to the fact that the previous marriage was not dissolved and a de facto marriage was formed with others.
According to the relevant judicial interpretation, if a person with a spouse lives with others in the name of husband and wife, or knows that others have a spouse and live together in the name of husband and wife, he should still be convicted and punished for bigamy.
If bigamy constitutes a crime, criminal responsibility shall be investigated according to law. According to Article 258, whoever has a spouse commits bigamy, or marries someone knowing that they have a spouse, shall be sentenced to fixed-term imprisonment of not more than two years or criminal detention.
To sum up, the evidence you want to collect is mainly evidence that can prove the following two points:
1. People with spouses live together with others in the name of husband and wife;
2, knowing that others have a spouse and marry them or live together in the name of husband and wife.
Living together in the name of husband and wife is mainly proved by relatives and friends.