Attleboro Police Chief Kyle Heagney told ABC News he read about the incident in the local newspaper and "the note was officially passed to us, 8 a.m. Tuesday morning, a week and a day later."
ABC reported parents with children at Hill-Roberts Elementary School went to the newspaper because they weren't satisfied with administrators' handling of the matter.
A substitute teacher at the school found the note, with the words "To Kill" in big block letters at the top on Feb. 3. It contained "less than 12 but more than half a dozen" names with check marks next to a few and others crossed out, Heagney said.
"As the chief of police, I'm concerned no one inquired whether this boy had access to firearms," he said.
"A 9 year old can kill with finality just as an adult can. We are still dealing with a very real threat. ... I'm disappointed that we weren't notified in an expedient fashion."
ABC said School Superintendent Kenneth Sheehan said in a statement he felt confident all students involved in the incident are safe and he "will continue to take the necessary steps to keep them safe." The student suspected of writing the note was to undergo a risk assessment with a psychologist to ascertain whether he is dangerous.
"A very thorough investigation is under way and all of the appropriate people and agencies will be involved," Sheehan said.
Heagney said the test results will determine whether the boy is allowed back into the school and steps were being taken to ensure authorities are alerted in any future incidents.
"We are looking at what his overall intent was, the ability to carry out that threat, and the opportunity," the police chief said.