A man has told a coroner he went to the police after the mother of the Kahui babies told him, "I did it."
No-one has been held responsible for the deaths of three month old twins Chris and Cru Kahui from traumatic head injuries in 2006.
Their father, Chris Kahui, was acquitted of murder in 2008..
Eru Tuari told a coroner at the boys' inquest that he started dating Macsyna King after her sons' deaths in 2006.
He said in early 2007 Ms King became upset and declared "Chris didn't do it, I did."
He said he went to the police with his concerns seven months later because he felt sorry for Mr Kahui.
"I know what jail's like, I've done it most of my life, and what I heard from her and what ... I heard on tele ... I just felt sorry for him."
The coroner heard that Mr Tuari taped Ms King on a mobile phone but police were unable to recover the recording when he told them about it seven months' later.
The hearing has run for about five weeks and has been adjourned twice since starting in October last year.
The inquest formally ended on Thursday afternoon, but the coroner will take further submissions in writing from lawyers before making his findings.