The report was ordered by then-Southern police district commander Paul Basham in August, along with an admission that police "missed some steps" after the 3-year-old was found dead in an oxidation pond in Gore in 2019.
The initial investigation concluded Lachie walked the 1.2km from where he was last seen to the pond, but his father Paul Jones has always disagreed.
Supt Basham tasked one of the police’s three national investigation leads, Detective Superintendent Darryl Sweeney, with providing a "senior and objective analysis" of the original investigation and the subsequent reinvestigation by Detective Inspector Stuart Harvey.
Det Supt Sweeney said it was essential the start of an investigation was well led, but this "did not occur to the required standard" in the case of Lachie’s death.
That was "not through the fault of any one particular individual", but because of a lack of senior leadership from the Criminal Investigation Branch (CIB), and insufficient communication.
Although some aspects of the initial investigation were done "reasonably well", best practice was not followed in managing the scene, the postmortem and forensics.
A CIB officer should have taken charge on the night of Lachie’s disappearance, and the area around the pond should have been cordoned off and a better scene examination undertaken the next day.
A lack of formal, detailed briefings on the night and the following morning led to an "information gap" that resulted in those failures.
By the time of Det Insp Harvey’s reinvestigation in late 2020, it was too late to "recover" the scene examination and carry out a forensic postmortem of Lachie, Det Supt Sweeney said.
"It is difficult to ascertain ... what evidence might have been missed, but the available facts tend to point to Lachlan walking into or falling into the pond."
Det Insp Harvey’s reinvestigation had focused on Lachlan’s half-brothers Jonathan and Cameron Scott, and there was no evidence to suggest that either was involved in Lachlan’s death.
Lachie’s mother, Cameron Scott and a neighbour all told police the 3-year-old liked to run away and hide or be chased.
There were indications of "risk behaviour" in the household regarding drugs, alcohol and the driving of a car with Lachie as a passenger, but no information indicating police or Oranga Tamariki had needed to be involved with the family before Lachie’s death.
The standard of care by his mother "might arguably be regarded as negligent in some minor areas", but did not raise issues of criminality.
Det Supt Sweeney said the police considered Lachie was likely the victim of drowning, and there was no evidence pointing to any person being directly or indirectly responsible for his death.
