New Haven, Connecticut (CNN) The principal's voice piped through the PA system at Wilbur Cross High School with a startling announcement.

ICE had detained a student.

"Everyone was worried and asking around," says Sandy Martinez-Paz, a 17-year-old junior at the school. "We wanted to know who it was."

Students later learned that Mario Aguilar, an 18-year-old who enrolled in the school last year, was arrested by Immigration and Customs Enforcement officers at a nearby courthouse where he'd gone to face charges after a traffic accident.

It's the kind of case that unfolds frequently across the United States, but often goes unnoticed or quickly fades from view.

At Wilbur Cross, something different happened.

The school where many were still getting to know Mario began fighting to bring him back.

Teachers bundled up homework to send to Mario in ICE detention, hoping their student wouldn't fall behind or feel forgotten. They wrote letters pushing for his release. And they showed up to support him in court.

Students designed "Free Mario" protest posters in the school's print shop. They put his face on a sticker and sold it to raise money for his commissary. And for weeks, they kept his desk in Spanish class empty, hoping he'd return.

A bulletin board dedicated to Mario Aguilar hangs in the hallway at Wilbur Cross High School in New Haven, Connecticut. Since ICE detained him in September, students, teachers and administrators at the school have been pushing for his release.

Now Mario's supporters at the school are anxiously awaiting an immigration judge's ruling in his asylum case and planning next steps in their push to free him -- undeterred by the fact that so far, their efforts haven't swayed authorities.

Many feel the dangers of doing nothing are far too great. If Mario's deported to Guatemala, a country he fled, they fear it could be a death sentence.

And if they don't stand up for him, they fear that no one will.

He went to court alone and left in ICE custody

Mario Aguilar headed to court in Milford, Connecticut, alone on September 10 to face the charges against him.

After a car accident a month earlier, police had arrested him on suspicion of driving under the influence, operating a motor vehicle without a license and failure to insure a private motor vehicle. They released him from custody on a promise to appear in court.

Advocates for the teen say he crashed into a parked car after his cell phone slid off the dashboard and he reached down to pick it up. They argue a sobriety test was never performed and the DUI charge wouldn't have held up in court.

But a state court judge never had a chance to hear that argument.

As the 18-year-old got into line at the courthouse, someone said his name.

He turned around, and moments later, he was in ICE custody.

Liz Demsky, a school counselor at Cross, keeps a #bringmariohome sticker on her phone. She says she's worried about a judge's upcoming ruling in his case. "I'm scared what's going to happen with the students here. How's it going to affect them?"

"Deportation officers arrested Mario Andres Aguilar-Castanon, an illegally-present citizen of Guatemala, at the Milford Superior Court for immigration violations," ICE spokesman John Mohan said in a statement, adding that removal proceedings are pending.

Mohan said the teenager was arrested by US Border Patrol agents near the Southwest border in March 2018 and issued a notice to appear in immigration court before he was released from custody.

"He failed to appear in immigration court," Mohan said -- a claim Mario's lawyers dispute.

They say Mario was 16 years old when he came to the United States from Guatemala in 2018 as an "unaccompanied minor," the US government's term for children who cross the border alone, without parents or guardians. And that he isn't aware of receiving any paperwork about a court date when he was released from US custody.

No one at Wilbur Cross knew any of this the week of September 10. At the high school where he was taking classes like Geometry, Modern World History and Band, only one thing was clear. Mario had been at his desk on Monday. By Tuesday, he was gone.

For days, the school thought he had gone missing

Mia Breuler still remembers the dread she felt when she learned her student had disappeared.

She frantically searched for him for days.

The school counselor knew it wasn't like Mario to miss so much class, or to stop showing up at the store where he worked stocking shelves.

She called everyone she could think of as questions raced through her mind.

Was he in an accident? Had gangs attacked him? Or had he gotten into some kind of trouble?

There was no sign of him at local hospitals. Police didn't know where he went either.

Counselor Mia Breuler called hospitals and local police after Mario went missing. Days later, she learned he was in ICE detention.

"One officer said to me, 'Are you sure he's not with a girlfriend or something?'"

Breuler knew that wasn't what happened, but still, there was no sign of her student.

A missed call Mario's cousin got from a Massachusetts number eventually led the counselor to call the Bristol County House of Corrections in North Dartmouth, Massachusetts, where officials confirmed Mario was being held.

That, Breuler says, was a "triage moment."

"It was shocking on all sorts of levels. It was very upsetting. I was anxiety-ridden because I was thinking, 'Now what do I do? ... Where do I go? ... Where do I begin to try to get help for this kid?'"

Unable to reach his family for weeks, Mario called his school instead.

Breuler spoke to him almost every day.

When she heard his voice, she didn't let her anxiety show.

She asked if he felt safe. She told him not to give up hope.

She wanted him to know he wasn't alone.

The principal got emotional about her missing student

Wilbur Cross Principal Edith Johnson stood on the steps of New Haven's City Hall, wearing a jacket with the school's official colors, red and white.

"Cross pride!" the crowd shouted as she took the microphone. Students around her cheered.

But the mood turned somber as Johnson began to discuss how Mario's detention had shaken her.

"Our school community is suffering," Johnson said as local news cameras rolled . "He is missing from our classrooms, from our hallways, from our cafeteria."

Photos and signs about Mario's case aren't the only calls to action on the walls at Wilbur Cross. A Mahatma Gandhi quote is painted on lockers on the third floor of the school.

Johnson didn't plan to get emotional at the rally that day in October. She's been the principal of Wilbur Cross since 2013. And as the leader of a school with some 1,600 students, she's seen many struggling to deal with trauma. But nothing like this -- a student being detained by ICE -- had ever happened during her time there.

As she spoke of her student, she began to think of her own family's story -- of how her parents struggled when they came to New York from Puerto Rico in the '40s and '50s. She thought of how lonely and scared Mario must be in detention, and how eager he'd seemed to learn. The tears began to flow.

She told the crowd that in her career as an educator and administrator, she'd lost far too many students to violence and tragedy.

"And now, another terrifying variable certain to take students off course," she said , "ICE arrests."

Mario's teacher attended his asylum hearing

The day Mario made his case for asylum in a Boston immigration court, Mary Perez Estrada saw him from across the room and waved.

The Spanish teacher's heart sank as she saw him try to lift his hand to wave back. He couldn't. His hands were shackled.

Spanish teacher Mary Perez Estrada says she thinks of Mario every day when she looks at her attendance sheet. His name is the first one on the list.

It was a week before Thanksgiving. Mario had only been in her class for a few weeks when he was detained, but she'd already seen his promise as a student. The way he'd ask questions and take on extra work particularly stood out. He'd told her he dreamed of becoming a biologist. On a questionnaire she had students fill out at the beginning of the year, when asked to describe something interesting about himself, he wrote, "Me gusta trabajar y esforzarme, a pesar de estar solo en este pais." I like to work and strive, despite being alone in this country.

When the school's assistant principal asked teachers to gather homework to send him, Perez Estrada pulled out books from her personal collection that she hoped would help his mind escape, even if he was trapped inside a detention center's walls.

She wrote smiley faces inside the covers to keep his spirits up.

She thought of him every morning in her homeroom, and each time she taught her third period Spanish class. His last name -- Aguilar -- is still first on the attendance list. For weeks, students kept his desk empty, hoping he'd return.

As Mario spoke before the court, detailing how he'd fled persecution from gangs in Guatemala, Perez Estrada hoped the judge would see what she did in her student -- someone who deserves a chance.

The judge didn't make a ruling that day. He told the court he'd announce his decision on December 12.

Perez Estrada headed outside to share what she'd seen with dozens of students and activists who'd been waiting for word on what had happened.

Some 1,600 students attend Wilbur Cross High School. Principal Edith Johnson says she was shocked to learn ICE had detained a student. "I just remember thinking, 'Wow, this is way bigger than me, way bigger than the school. This kid really needs help.'"

"Mario we love you," the students chanted before they piled back onto a bus to return to New Haven.

"Mario we're with you.

"Mario we are fighting with you.

"We believe in you.

"We got you.

"Every day.

"Even after today.

"We will stand with you.

"Because we love you.

"Because you're family.

"Because you're our community."

Inside, they hoped he could hear their voices.

Students are making a video to share his story

Gabriela Gonzalez didn't know Mario before. Most students didn't, she says. But lately, she's been spending a lot of her free time learning his story.

The senior at Wilbur Cross studied filmmaking for years as a student in the school's International Academy of Digital Arts & Sciences. Now she's helping make a film for a schoolwide assembly to teach her classmates about this case and why it matters.

In a conference room near the principal's office on a Friday afternoon, she peppers students from the school's "Cross in Action" immigrant advocacy group with questions.

"Why is this important?" she asks.

"The kids in school are stressed and worried because it's close to home," one student replies. "And they're scared because they probably think, 'What if I'm next?'"

Gabriela Gonzalez, a senior, says she's learned a lot while making a film about Mario's case. "It's helping get the story out there," she says, "so that people are finally aware of what's actually happening right in front of them in their own communities."

"It's a story that should be heard all over. It's something that it isn't new. It hasn't just started happening. It's something that's going on around the whole country," another student says. "And everyone needs to know the reality people that come here face. It's not like it's easy for them. They go through so much and people don't understand or don't see it."

As she takes a break from an afternoon of interviews, Gonzalez notes that only Mario's closest friends knew him before. They've shared stories with her about how they'd walk to school together or go out to eat. But now, she says, even students who never met him can see the symbolism in his story.

"He wasn't known before, but now literally there's posters around the school with his face on it everywhere. People didn't know about him because he was just a regular student. ... But now the fact that just this ordinary student was taken, his whole life has been turned upside down because he happens to be from somewhere else, shows that this can happen to anyone," she says.

"And it shouldn't happen to anyone, because we're all just trying to live our lives as teenagers or normal, everyday people walking around the street."

His homework was 'refused' and returned to sender

An immigration judge in Boston is weighing Mario's fate. His supporters had expected the judge to rule on Thursday, but instead learned in court that he'll be issuing a written decision soon.

If the judge denies Mario's asylum claim, his lawyers say they'll appeal the ruling and keep fighting the government's efforts to deport him.

And in the meantime, if he remains detained, they say they'll keep trying to get homework to him.

So far, they haven't had any luck.

Attorney Dalia Fuleihan says she tried to send the homework to the Bristol County House of Corrections -- first in an in-person meeting with her client, and then via US mail after she was told she could only hand him legal paperwork.

English language teacher Cynthia Clampitt wrote instructions for Mario on sticky notes in the homework packet she sent him.

She got the envelope of homework she'd sent back last month, stamped "Return to sender. Refused." A handwritten note on the stamp said, "Unknown name" and "ID# required."

Asked why the homework was returned, an ICE spokesman said the agency doesn't comment on issues, claims or allegations that "are not related to a detainee's enforcement status."

Back at Wilbur Cross, Mario's teachers say they're shocked he didn't receive the homework or the books they tried to send him. To them, it's another reminder that their student belongs in a classroom, not a jail cell.

Fuleihan has the returned envelope at her office at the New Haven Legal Assistance Association as she sorts out next steps. Inside it, for now, the teachers' messages remain unread.

One teacher scribbled out instructions on yellow sticky notes placed on different pages in the packet.

She put an assignment Mario started on one of his first days of class at the top of the pile, titled: "Who Am I? My Past, Present and Future Hopes and Dreams."

On the first page, Mario wrote his name, stated where he was from and drew a picture of himself.

He noted that he liked music and disliked avocados.

"Mario -- Finish!" the teacher's sticky note says. "This is important."

The pages describing his future are still blank.