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.
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.