Yes, the sentence "There is no strong forensic evidence. There's only testimony from witnesses and the victim and it doesn't match" is correct in a police context. The phrase "it doesn't match" is a natural way to say that the testimony from the witnesses and the victim does not agree. Here are some other natural ways to say the same thing: "The testimony from the witnesses and the victim is inconsistent." "The witnesses' stories don't line up." "The victim's account of the events differs from the witnesses' accounts." The phrase "none of the testimony matches" is also correct, but it is a bit more formal. It is also possible to say "the testimony is contradictory" or "the testimony is conflicting." The best way to say it will depend on the specific context. If you are talking to a police officer, you might use the more formal phrase "none of the testimony matches." If you are talking to a friend or family member, you might use the more informal phrase "the testimony doesn't match."

Interesting questions. You could say: "The investigation yielded no forensic evidence, and the testimony from the witnesses and the victim were contradictory." 'Inconclusive' is another word to describe evidence, but it has a neutral connotation...i.e. just not enough info to draw a conclusion. If witness testimony is 'contradictory' that could be neutral (i.e. in stressful situations people can have faulty recollection of events) or possibly it could allude to one party lying. 'Inconsistent' is similar to contradictory but more neutral, less severe, maybe. If you thought something nefarious/bad was happening, you could say 'suspiciously contradictory.'

Since "testimony" is a singular noun, you cannot say it doesn't match. Only two or more things can match. One person alone gives a testimony. The word "testimony" is closely related to the verb "to testify". You can say "their testimonies do not match" or "their testimonies are inconsistent" or "their testimonies conflict".