Blood-splattered wet wipes, bedding and footage from a sophisticated CCTV set-up could hold clues to who killed the toddler Nga Reo Te Huatahi Reremoana Ahipene-Wall, known as Baby Ru.
Ru died at Hutt hospital in October from blunt-force injuries. The police say there were three people in the Taita house at the time the little boy was fatally injured.
Detective Inspector Nick Pritchard says it is time for the truth.
"We know all three have knowledge about what happened in that house, and we would really urge them to come forward and be open with us so that we can give some closure to the family of Baby Ru," he told Checkpoint on Friday.
Those three were Rosie Morunga, her partner Dylan Ross and Ru's mother, Storm Wall.
"We've been engaging with them from the outset and they have been cooperative with us, but we are not getting a full account from them in terms of what happened inside the house," Pritchard said.
Police are getting a number of items tested forensically, including bloody wet wipes, bedding and clothing. Blood from elsewhere in the house was also being investigated to see if it came from Ru.
It remains unclear if Ru had been administered illicit drugs before he was taken to Hutt Hospital in an unresponsive state on 22 October. When he arrived, he was wearing "a piece of fabric tied in a knot" around his neck, Pritchard said - just why remained only known to those he lived with.
"That's something that someone else inside that house will know and I'd really like them to come forward and tell us why it was on the child and what its purpose was."
Investigators were also appealing for help tracking a Nissan Sentra sedan they believe was used to take evidence away from the property, including a hard drive that could contain footage from several cameras - including one that was recording inside the house.
"That vehicle has travelled back to the address in Paul Street three times in between the first trip to the hospital and before police were notified of this death, and had the opportunity to seize the property with a search warrant...
"During one of those visits, some items have been removed from the property which are of relevance to the investigation, with one being a DVR recorder which monitored CCTV at the property."
The "incredibly sophisticated" setup was capable of monitoring several feeds at once, he said, and it remained unclear why they had it.
"There [were] several cameras, majority were recording outside. There was one in the hallway and that's the one that is really of interest to us - certainly would have captured things that would be very helpful to our investigation."
The car police are wanting to track is a Nissan Sentra, Licence plate TE6972. If you saw the vehicle anytime from Sunday 22 October to Tuesday 24 October, police would like to hear from you.
Anyone with information should contact police on 105 quoting file number 231022/1708 or anonymously via Crime Stoppers.
No one has been charged yet over Ru's violent death.