How Long To Adoption Agencies Follow Up With Adoptive Parents

I was reading about the Hillside Stranger, - Ken Bianchi and he was adopted (like all serial killers are :)) anyway the book had copies of reports filed by his adoption agency.

Now it says the adoption agency had finalized the adoption just before he was one year old. But then the book produces reports which follow up with the parents, when he’s 5 years old, 7 years old, 10 years old and even after his father died when he was 13 years old.

So I was wondering just how long do the agencies follow up on the babies they place?

Actually this wasn’t an agency, it was the state of New York. His birth mother put him in foster care right after birth and the adoptive mother got him through foster care then adopted him that way