IRVINGTON, Calif. – Seniors at Irvington High School were forced to spend their last day of school scrubbing graffiti off sidewalks on campus, including a giant swastika spray-painted in the courtyard Sunday as part of an overzealous senior prank.

About four dozen seniors vandalized the Fremont campus by spray-painting obscene messages around the school, draining the swimming pool and tossing in assorted pipes and other junk, and plugging many of the classroom doors with clay to prevent staff from getting inside, the East Bay Times reports.

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“This is highly offensive, inexcusable, and there’s nothing that you can say to defend what is essentially hate speech,” Fremont Unified School District Superintendent Jim Morris told said Tuesday. “There is no excuse for it.”

First thing Monday morning school and district officials called all Irvington seniors to an assembly to force them to clean up the mess.

According to The Voice, the school’s student news site:

Standing in front of brooms, buckets, and cleaning supplies, Principal Sarah Barrious said to the seniors, “[I]t’s not a senior prank. It’s vandalism. There’s permanent damage done. For those of you who weren’t involved, and I know it was a small group, there’s super glue and putty that will cause thousands of dollars to fix. In public education, where we already don’t have money.”

She continued, informing the class that there were only two daytime janitors, and that the seniors would need to clean up the campus with the supplies she had in front of her.

The principal also addressed the situation in a video posted to The Voice’s Facebook page.

“The images and the words that are on the walls of Irvington High School are not something I want in the media,” she said. “It does not reflect well on me, or you, or this community. We have to clean it up.”

School officials divided the roughly 450 students into teams and dispatched them throughout the campus early Monday as janitors put down kitty litter and powder to absorb the oil in the school hallways.

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“The prank included a large rainbow thank you message to AP Calculus teacher Ms. Chung (which the administration instructed students to leave alone); a green swastika painted in the courtyard; carious warnings about QUEST, Irvington’s senior benchmark project; a displaced handicap sign; and pipes and obscene writing in the pool,” according to the Voice.

By around 9 a.m. Monday, students had cleaned up most of the damage to the outside of the school and shifted their focus to the large swastika in the courtyard, where they worked in the rain using their fingernails, coins, ID cards and metal pieces to scrape up the paint.

About a half hour later, the school hallways were clear and much of the graffiti was removed and school officials ordered seniors back to class.

“As the day went on, some members of the administration pulled seniors out of class or looked through confiscated phones in an effort to find the group of seniors that carried out the prank,” the Voice reports.

“During sixth period, a senior hacked the marquee to show memes and a statement cancelling finals for all grades. The school reversed this prank by around 3:00 p.m.”

Barrious said officials are continuing to investigate the incident to track down the students responsible, but will not press criminal charges. Those students will also be allowed to participate in the school’s graduation ceremonies on Friday, but likely will not receive their actual diploma until all of the damage is resolved.

Several students who were not involved with the prank voiced their frustrations on Facebook.

“For everyone who participated in the vandalism and destruction of school property who wanted to do something that would be remembered, we’re all going to remember this all right, but not in a positive light, not after having to clean up the mess caused by your stupidity,” senior Mitchell Hogle wrote, according to the Voice.

“I used to boast about Irvington for being one of the most accepting and tolerating high school communities in our country … but today was eye opening,” senior Samiha Uddin posted. “I am still in shock that I will forever remember my last day of high school as furiously having to scrub off a swastika off the courtyard floor.”