Search warrant needed when you have permission?

Factual Questions
1

Is a search warrant still needed when you have the owners permission to enter?

From this article about a man who found a mummified baby from 1925 in a house he was renovating:

It’s not clear if the renovators were working on someone else’s house, or if the renovation company itself owned the house, but I would think that in either case the owner would be happy to let the police in to remove the dead baby remains. Was it some kind of standard procedure to get the warrant, or did it have to do with the fact that a non owner found the baby, or is it likely that the owner refused entry for some reason? Is it possible the police got the warrant without trying to contact the owner first?

2

It could be that the owners were not available to grant permission. (If they were renovating they may have been out of town or something.) Or, since there was probably no need for expediency, the police may have decided to have all their bases covered before doing the search.