Also today, the family of one of the five killed issued a statement honoring the victim, Shirley Timmons.
Santiago, 26, wore a red jumpsuit with shackles binding his wrists and ankles. He sat expressionless, hunched at the defense table during the proceedings, with U.S. marshals standing behind him.
Judge Alicia Valle read the federal charges against Santiago: performing an act of violence against a person at an airport that caused serious bodily injury, causing the death of a person through the use of a firearm and using and carrying a firearm in a crime of violence.
Santiago was informed in court that if he is convicted, he could face the death penalty, and Valle appointed a public defender, Robert Ruby, to represent him.
Santiago did not enter a plea in court today. Prosecutors asked for pretrial detention, a request that will be heard by a judge Tuesday, Jan. 16, at 1 p.m. That will be followed by a hearing on Jan. 23.
The family of Shirley Timmons of Ohio issued a statement Monday. She was shot and killed in the attack, and her husband, Steve Timmons, was critically wounded, according to The Associated Press, which cited radio station WILE-FM.
"Shirley Timmons was an amazing daughter, wife, mother and grandmother," said the statement. "For Shirley, it was all about family. She and her husband of 51 years met when they were in the 8th grade ... Together they built a close, loving family with their three daughters, three sons-in-law and eight grandchildren."
Santiago, who has been held without bail since his arrest Friday, told investigators that he planned the attack and bought a one-way ticket to Fort Lauderdale to carry it out, according to an FBI affidavit.
Investigators have found no reason he allegedly chose the Fort Lauderdale–Hollywood International Airport as his target. They also haven't determined a motive for the shooting, which took place Friday just before 1 p.m. Eatern time in a baggage claim area, according to George Piro, the special agent in charge of the FBI's Miami office.
"We have not identified any triggers that would have caused this attack," Pirro said at a news conference Saturday morning. "We're pursuing all angles on what prompted him to carry out this horrific attack."
Santiago said in court today that he is largely destitute and that before the shooting, he was paying about $560 a month in rent and $50 per month for his phone. He identified no other major expenses and had $10 dollars in his bank account, with no other savings.
He last worked in November, when he was employed as a security guard for Signal 88, a company that provides security services. His employment before that was with the Army.
ABC News' Morgan Winsor, David Caplan, Matt Foster and Dominick Proto contributed to this story, which was supplemented by Associated Press reporting.