Federal investigators are continuing a probe into whether “Empire” actor Jussie Smollett was involved in sending a threatening letter he received on the set of the show, even as 16 felony counts for filing a false police report were dropped by Chicago prosecutors.

Chicago Police Superintendent Eddie Johnson said at a press briefing in February that detectives found evidence that Smollett was behind a letter he received on the set of “Empire” that contained threats. “Empire” is filmed in Chicago.

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.

NEW: From @ABC @JoshMargolin: The FBI and US Postal Inspection Service are continuing their probe into whether Jussie Smollett played a role in sending a threatening to himself prior to the allegedly staged attack, according to a law enforcement official briefed. 1/2 — Rob Elgas (@RobElgasABC7) March 26, 2019

MORE: The federal investigation, originally confirmed by @ABC on Feb. 20, has remained open all along–even after the “Empire” actor was hit with Illinois state charges. Developments today have no impact on the federal probe. The FBI’s Chicago office declined to comment. 2/2 — Rob Elgas (@RobElgasABC7) March 26, 2019

While the FBI declined comment, the U.S. Postal Service told Fox News that investigators are working on the probe.

“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: “When the letter didn’t get enough attention, he concocted the staged attack” – CPD sources. Jussie Smollett received a hate letter Jan. 22. It’s that letter, the mail angle, that brought in the FBI. “That makes any potential case a Federal one, if they want it.” pic.twitter.com/dTk2ECBvhU — Brad Edwards (@tvbrad) February 19, 2019

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.