The ministry investigates all complaints about legal aid lawyers. In King's case they examined invoices and allegations he'd over-billed.
King defended the prisoner, who has name suppression, at his High Court jury trial in Wellington in September 2011. The man, in his early 50s, was convicted of 19 sex offences against six young people.
The charges included rape, indecent assault and doing indecent acts.
The man maintains his innocence. He is serving a preventive detention sentence but is fighting to have his conviction overturned and a retrial ordered.
He contended the hours put in for Milnes-King, who had acted as second counsel in the case, were inflated.
He wrote to the Herald on Sunday outlining his concerns, including serious misgivings about King's handling of his case.
Milnes-King declined to comment.