The woman, who did not want to be named, and her 19-year-old son with Molenaar were living in Auckland. She had ended the seven-year relationship 15 years ago, but he had got back in touch with his son in 2003 after the suicide of his brother, the Sunday Star-Times reported.
"He was civil and fine the last couple of times I had seen him. I know he cared about (his son) a lot," she told the newspaper.
Claims by Molenaar's brother Peter about a recent dispute over contact with his son were wrong, but she had no knowledge about anything that would have made him react as he did.
"We have no understanding of it. We've been in no way involved in his personal life, what he's been doing. I'm not going to speculate."
However, she said Molenaar would have regretted the way events escalated.
Molenaar had texted his son a couple of weeks ago saying; "have a good day, love you," but the young man would not comment on whether he had been in contact with his father during the siege.
A friend told them about what was happening on Thursday shortly after the siege began, and they had been watching events unfold.
"It's been horrifying for us," she said. "It's just hard to know someone you've known is capable of what happened."
Molenaar was found dead when police entered the house late yesterday morning. He had kept police at bay since Thursday morning, after the shooting of three police officers and a neighbour following what was thought to be a routine cannabis inquiry.
