The agent did not elaborate on whether Santiago was purporting to be linked to ISIS or simply inspired by the terrorist organization.
Federal authorities in Alaska said Santiago told them prior to the attack that he was hearing voices and that his mind was being controlled by the CIA. Santiago initially made similar claims during an interrogation following the shooting, but once he was transferred to the FBI office in Miramar, Florida, Santiago introduced the ISIS claim and never again mentioned mind control, Ferlazzo testified.
ISIS has not claimed responsibility for the January 6 attack at Fort Lauderdale-Hollywood International Airport.
Ferlazzo, who conducted the interview in Miramar, said only that Santiago claimed to be fighting for ISIS and that he'd been in touch via jihadi chat rooms with like-minded people who were planning attacks as well.
Santiago is charged with using and carrying a firearm during and in relation to a crime of violence; performing an act of violence against a person at an airport serving international civil aviation that caused serious bodily injury; and causing the death of a person through the use of a firearm.
The latter two are punishable by death, while the first charge carries a maximum penalty of life in prison.
Authorities have said that Santiago confessed to the mass shooting, which they said he perpetrated after disembarking a plane from Anchorage and collecting a checked bag containing a Walther 9 mm pistol and two magazines.
At Tuesday's hearing, the defense did not argue the prosecution's assertion that Santiago posed a flight risk, as well as a danger to the community, and said that the defendant was prepared to be detained throughout his trial.
The judge ruled he be held without bond. His next court appearance is January 30.