Are they using public scanning now? It's the only way, but the article says nothing.
That is probably not how they found him. Police very rarely want to disclose their real methods or sources.
Most likely they used contact tracing with a database of cell phone call records. If he ever called a relative or former friend in 30 years he would be traceable.
And of course there is always the classic informant who knows something about a person of-interest.