A US judge has blocked the suspension of a high school girl who was punished for posting a note at school warning of a “rapist” in their midst.

In September Aela Mansmann, 15, was accused of bullying by school officials in Cape Elizabeth, Maine, after she posted notes in the girl’s toilets.

But on Thursday a judge issued a temporary stay on the suspension citing concerns over free speech rights.

A lawsuit filed by the girl’s family against the school is still pending.

The case began on 16 September after Aela posted notes in two bathrooms at Cape Elizabeth High School reading: “There’s a rapist in the school and you know who it is.”

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After another student brought the note to school administrators, they investigated and identified Aela through camera footage.

She and two other girls were suspended for three days on 4 October after officials determined the behaviour constituted bullying.

The district’s investigation revealed that one male student felt targeted by the notes and was ostracised by his peers, forcing him to miss classes.

In an interview with CBS, Aela said her note was never intended to single out anyone as a rapist, but was rather highlighting the issue of sexual assault.

The Bangor Daily News reports that after the notes were posted, “the rumour mill spun out of control, creating fear in the high school”.

The principal, Jeffrey Shedd, conducted 47 interviews and determined the school was safe, according to the newspaper.

He previously said the three girls who were suspended “made a really bad choice”, despite meaning well.

Her suspension led about 50 students in the 550-pupil school to walk out in protest on 7 October.

The American Civil Liberties Union (ACLU) sued the school district near Portland, Maine’s largest city.

It argued that the girl had simply taken a “public stance as an ally for victims and survivors of sexual violence”.

In the order temporarily blocking the suspension on Thursday, US District Court Judge Lance Walker cited “a fair likelihood” that the suspension will ultimately be overturned on the grounds of free speech and Title IX – a federal law that bans gender discrimination in education.

The notes, the judge wrote, were “neither frivolous nor fabricated, took place within the limited confines of the girls’ bathroom, related to a matter of concern to the young women who might enter the bathroom and receive the message, and [were] not disruptive of school discipline”.

He added that students have a right to feel safe knowing that a “student who expresses a comparable view in similar fashion will be denied access to school simply because her viewpoint offends the sensibilities of school administrators”.

The ACLU praised the decision in a press release on Thursday, saying: “Speaking up about sexual assault is already difficult for young people.

“If this punishment had been allowed to stand, it would have only made it more difficult.

“Today’s decision reaffirms that students have the right to freedom of speech, and that they do not check their rights at the schoolhouse gate.”

Shael Norris, the girl’s mother, also hailed the decision.

“All my daughter ever wanted was for students to feel safe speaking out about sexual assault,” she said in a statement through the ACLU.

“I’m so proud of her for standing up for what she believes in.”