(JTA) — A school district in Pennsylvania is investigating social media posts from students on a senior class trip that mocked exhibits at the U.S. Holocaust Museum.

The senior class from the Forest Hills School District visited the museum in Washington DC last Wednesday as part of its senior class trip.

Senior class president Gabe Singer told the Associated Press that most students were respectful. But some other students reportedly made inappropriate posts to social media, including disrespectful statements next to a photo of a pile of shoes take from Holocaust victims at a Nazi concentration camp that was posted on Snapchat. Those students “made a mockery of what they saw,” Singer told AP.

In a public letter Singer apologized on behalf of his classmates and called their actions “unacceptable,” according to the AP. He said he hoped that students who come after his class will still be able to visit the museum.

Forest Hills School District Superintendent Edwin Bowser told the Associated Press on Friday that school officials are looking into the students’ conduct.