An investigation is under way to find the source of a threatening letter sent to a family whose son -- along with four other boys -- stirred up controversy after they cut down trees as a prank at Central High School East campus, Fresno Police Chief Jerry Dyer confirmed Friday.
All five families reported receiving the same anonymous letter, which warned "watch your backs."
A press release from the Police Department said one family contacted the department Thursday and was interviewed by an officer, launching the investigation.
Police also said a law enforcement report has been written on the tree-cutting incident that took place the night of Feb. 4.
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Fresno police are "allowing the Central Unified School District to resolve the matter with the students," the statement from Dyer said.
The five students, all seniors, admitted using a saw to cut down two nearly 20-foot-tall Southern live oak trees.
While the students called the incident a prank, district officials called it vandalism that could cost $7,500 to $14,000 to repair.
The tree-cutting incident became public after parents and their attorneys announced they were challenging action taken by district officials, who suspended the students for a week and then transferred them to a continuation school.