The family of murdered Whangarei woman Ashlee Edwards say her killer's guilty plea is a massive relief.

The body of the 21-year-old mother-of-two was found under a bridge in July 2012.

Her former partner, Jimmy Akuhata, was arrested for her murder and yesterday admitted the charge.

An IPCA report into the death severely criticised police for its investigation after they mismanaged the victim's complaints her killer had been breaching protection orders.

Days before her death, she warned police Akuhata had breached an order and threatened to kill her.

Ashlee Edwards' mother Karen Edwards has posted on Facebook, saying it's been a horrific nightmare and caused sheer utter heartbreak.