I guess he tried to point out that BTC adresses are resolvable and one could create a profile of pm1957's use of Bitcoin.
Tracking adresses to businesses or individuals would be the simplest thing within the scope of that topic.

EDIT: And as soon as you have a single transaction successfully mapped to the receiving individual, you could do things like call the receiver and "hi, this is agent herold bloblobrob from the fbi. You were receiving bitcoins a couple of years ago that were stolen. Can you look up/remember this transaction and possibly identify who sent it? For the love of your country..."