Continuing with 'The Ultimate Evil' from Maury Terry...

... In July 1981 an apprehensive David Berkowitz was unexpectedly transferred from Attica to the Clinton Correctional Facility in Dannemora, New York. Located in the northeast corner of the state near the Canadian border, the ancient gray behemoth was the most inaccessible prison in the system. Left behind at Attica, to John Santucci's chagrin, were valuable informants. But ahead at Dannemora were others, more than one of whom was eventually removed from that facility and separated from Berkowitz.

Frankly, the succession of moves was suspicious and would be noted as such by the district attorney's office and myself.

These prisoners, and one prime outside contact, provided important information about the case. All knew Berkowitz well. To each, Berkowitz revealed intimate details, particulars which overlapped and were repeated to us by the informants, who were with Berkowitz during time periods ranging from 1979 to 1985.

To protect these sources, who may someday be asked to testify in a court of law and whose lives may be in jeopardy, the information they provided will be attributed here to two composite characters, whom I will call Vinny and Danny. The real names and letters or statements from each of them are in the possession of the Queens district attorney, who developed two of them. Others were cultivated by me.

As the information contained common elements, the road to confirmations was a single one. This consistency enhanced the informants' credibility and that of Berkowitz, who, it turned out, was relating the same details he first described to us in 1979-80—but with one major difference. With his fellow prisoners, and others, he filled in blanks he'd left for us to decipher as clues.
https://exploringrealhistory.blogspot.com/2020/02/part-11-ultimate-evilfrom-belly-of-beast.html