A Boston police captain's son who authorities say plotted to detonate a bomb at a university was ordered on Tuesday to remain behind bars while he awaits trial.

Alexander Ciccolo was arrested July 4 after he received four guns from a person cooperating with the FBI, authorities said.

His father is veteran police Capt. Robert Ciccolo, who alerted the FBI after his son said he wanted to join the Islamic State group. The police captain was not in U.S. District Court in Springfield for his son's detention hearing Tuesday.

Ciccolo, 23, mouthed "I love you" to his mother, who was seated in the front row.

Assistant U.S. Attorney Kevin O'Regan argued that Ciccolo should be held in custody because he poses a danger to the public and is a risk to flee while he is awaiting trial.

Ciccolo is charged only with being a felon in possession of a firearm, but his lawyer said after the court hearing that he expects more charges.

O'Regan told Magistrate Judge Katherine Robertson that Ciccolo "came under the sway" of the Islamic State group, developed a hatred for Americans and then accepted the group's "call to action" and started making plans to kill Americans.

"He dedicated himself to killing as many people in the United States as he could," O'Regan said.

Prosecutors said Ciccolo came up with several plots, including killing law enforcement and U.S. military personnel, but then began focusing on a plan to set off a pressure cooker bomb in a university cafeteria during lunchtime so he could kill as many people as possible.

O'Regan said Ciccolo "went about implementing the plan" when he began talking with the cooperating witness about acquiring materials.

Ciccolo said he would get the pressure cooker and other bomb ingredients, inspired by the bombs used to kill three people and injure more than 260 in the 2013 Boston Marathon bombing, O'Regan said.

Ciccolo asked the cooperating witness to get him guns, authorities said. After he accepted four guns delivered by the witness on July 4, he was arrested, they said.

Prosecutors played a 9-minute portion of an FBI interview after Ciccolo's arrest. In the recording, he expresses his continued support for the Islamic State.

When asked by an FBI agent how he feels about the group, he replies, "They are a good thing."

He tells the agent the group is "freeing people from oppression."

When the agent presses him about the group's claim of responsibility for beheadings, he says, "The people that you see being executed are criminals. They're criminals. They're the lowest of the low."

Ciccolo's lawyer, David Hoose, asked the judge to release him into the custody of his mother and said he is unlikely to flee.

Hoose noted that the cooperating witness, working with the FBI, gave the weapons to Ciccolo at no cost.

The judge said even though Ciccolo is charged only with an illegal-weapons count now she has to consider the nature and circumstances of his arrest.

"He accepted delivery of four firearms with the intent of committing an act of domestic terrorism," she said.