The investigation, which is being handled by the FBI and the United States Postal Service, was not affected by prosecutors dropping the charges, reported ABC 7.
“The U.S. Postal Inspection Service is working closely with our law enforcement partners on this investigation,” the U.S. Postal Service said in a statement. “We are unable to provide any additional comment at this time.”
Smollett could face up to 10 years in jail if charged with postal fraud.
A Chicago Police Department spokesman said that all evidence Chicago officers gathered in the case was handed over to the FBI.
Johnson, the police superintendent, told reporters at the press briefing that Smollett initially only planned the bogus letter, and when it failed to draw attention he resorted to staging a fake hate crime.
Smollett blamed the alleged Jan. 29 attack against him on white supporters of President Donald Trump, but police arrested two Nigerian-American brothers who were extras on "Empire." One of the brothers was a trainer for Smollett.
The actor has neither explained how he got key details about the alleged attack wrong, nor apologized to the president or his supporters.
The letter that arrived at the "Empire" set contained letters that appeared to be cut out from magazines to form threats against the actor in addition to a crude drawing of a stick figure hanging from a tree.
One of the pieces of evidence taken from the brothers’ house was a magazine. Investigators also took a book of stamps from the house.
The letter also contained a white powder and prompted a police response on Jan. 22, the day it was received on the set. The white substance was later determined to be aspirin.