Well, initially it would have been treated as a runaway case, not a murder, so there would have been no reason to do that. In any case, they would have needed a warrant to seal the house, and at that point there was no probable cause so they would not have got one.
They were given permission by BD to do a search, which they did, and nothing unusual popped up, so it is not as though they did not look. They did have a search warrant for the car, and that turned up nothing.
After the initial warrants they likely were not able to get any more since further investigation probably corroborated SA's movements, meaning there was no time for him to have done anything. And he did not lie to them, they did not ask the right questions and misunderstood what he told them. As per the affidavits, BD's movements that morning were corroborated as well. They would not be able to just ignore that when submitting an affidavit for any additional warrants. Then there is also the evidence gathered from the phone, which likely showed that HD was using it after SA was already at his mothers house. That being so, they would not have had probable cause for further warrants, and that is likely why no additional warrants were obtained after the first batch.
