I understand that the judge can decide if a persons previous convictions or behaviour can be released in court as part of the evidence.
I understand that this must be used with caution, the fact that you murdered your first husband does not necessarily mean that you also murdered your second, and every crime should be judged without prejudice. However in a case like this where the accused has a long history of multiple complaints of violence, made not just by members of the public, but by fellow officers as well this should surely be admisable evidence even if none of the complaints went to court.
After the Soham murders, when it was later revealed that Ian Huntley had been the subject of several complaints of sexual misbehaviour, although none went to court, I thought it was agreed that in a case where there were multiple complaints from different sources this evidence was admissable.