NZME. News Service was permitted to access the court file under the condition the complainant and defendants were not named.
The Crown applied to have the officer stand trial with the other three but in February Judge Anna Johns ruled there would have to be two trials because the allegations against the policeman were separate from the others.
The judge said there was no suggestion anyone else was present during his reported attacks, which the victim said happenned up to twice a week.
"To have the defendant's matters heard with the others would unduly prejudice his trial, especially as allegations of prolonged family abuse would lead to feelings of disgust with members of the jury," his lawyer James Maddox said.
Judge Johns agreed.
The trial for the three other accused - on 18 charges between them - will start in November and the Crown eventually decided in May that "public interest points away from proceeding against [the police officer]".
Four charges of assault with a weapon and one of assaulting a child were withdrawn.
"The Crown is of the view the child's wellbeing may be jeopardised by a second set of proceedings. That is a risk the Crown is not willing to take," prosecutor Eliza Walker said.
But both defence counsel and the judge said there was no evidence of any great emotional toll on the young girl.
"I see keeping [him] separate as not ultimately putting any additional stress on the complainant," Judge Johns said.
Court documents alleged that between 2012 and 2014 the cop also used his police belt as a weapon against the girl.
The complainant told interviewers that in one instance he "whacked" her five times and punched her as she lay on the ground, before dragging her along the floor by her legging and striking her again with the belt.
But the court recognised the allegations against the other three defendants as being more serious.
The Crown outlined the most serious incident, which allegedly began with the girl being punched, hit with a stick and sat on.
The police summary said she was held down while someone grabbed an electric bread knife from the kitchen in a bid to cut off her nipple.
"Fortunately, the knife did not work."
Further incidents allegedly saw the young relative dragged around the house by her hair, with such force clumps were pulled out.
And she also reported times when she was punched and had her head smashed into a brick wall outside the church they all attended.
According to court documents there were times when she missed school to hide her bruises and she was sometimes too tired to attend because the defendant would wake her up in the early hours of the morning and force her to make pancakes.
"He told her if she did not listen he would chop her legs off," an alleged summary of facts said.
A police spokeswoman said the officer was initially stood down and placed on restricted duties while the matter was subject to investigation.
"Following a subsequent withdrawal of charges in relation to the matter, it was reassessed against the police code of conduct, but there was no evidence found to support any breach of the code. The officer has since returned to normal duties."
Because the charges were withdrawn by the Crown, rather than dismissed by the court, there is a possibility they may be re-laid.
