He said that he had learned from previous abductions, and that he was going to bury the next one.
This can be taken two ways, IMO.
1) That he is using 'bury' to mean 'I am killing the next one'.
2) He has killed before, but has not bothered to bury his victims bodies. He has learned that this is something he should do going forward.
If option 1 is determined at some point to be correct, then we will find that there are a lot of abductions out there where the victim is allowed to live.
If option 2 is determined to be correct (and I think this will be the case), then we will probably find a lot of victims prior to 1990 left in the open, maybe hidden but not buried, and afterwards found with some attempt at burial.
I hope like hell I'm wrong, but I think it's going to be a lot more than 10 or 15.