In the letter, the author identified as being a former military member. The letter said the constant fireworks set off by Cambodian residents in Mifflin Square Park were affecting the author's sleep and mental health.
The author then threatened violence against anyone if the fireworks continue.
"I own several guns that are locked up, but I want to take a gun and kill these individuals," read a portion of the letter.
Late Thursday night, Philadelphia police identified the author as a 79-year-old woman, saying she never served in the Marine Corps and does not have access to weapons.
"This literally is racial and ethnic intimidation because it's a who what, where, how. The only question is the when?" said Sarun Chan, executive director of the Cambodian Association of Greater Philadelphia.
He says it's still a targeted threat, and warned residents by canvassing letters in both English and Khmer.
No charges have been filed at this time.
Police say the case has been forwarded to the district attorney's office for review.