Police probably didn't have evidence of the truck earlier.
I felt at the beginning of the case, with the prosecution's claim that the victims died at the acreage, that the junior prosecutor wanted to in some ways sensationalize evidence found at the acreage regardless of whether it related directly to their deaths.
The ME was unable to say whether the victims died at the Liknes home, but the blood spatter expert had no problem describing the extensive blood loss and violence that one would assume meant that they very likely either died at the home, or died as a result of the injuries inflicted at the home. That is why I suggested that the ME favoured the prosecution when stating that she didn't know whether they died at the home or not ... either that, or she is inexperienced. Her testimony seems, in many ways, to be little more than a self serving support for the prosecution's claim that maybe the victims were still alive in the back of Garland's truck. That does not mean that they were alive at the acreage, but that is what the prosecution wants the jury to believe ... and that justified the introduction of all sorts of gruesome evidence that probably had no role in the murders.
The business about diapers seems completely irrelevant. Diapers were found on the acreage, and there is a photo of two of the victims wearing white underwear or a diaper. If doesn't matter what they were wearing. If they were photographed at the acreage, that is all that matters.
Of course they did not have the evidence earlier cause they STARTED TO COLLECT it on July 2nd! And this should have been their priority, especially in a case of amber alert, they know the stats and the race with time - the first 24h, after that time survival probability decrease significantly.