On Tuesday evening, the PSNI's public protection unit in Lisburn appealed for the public's help, through Facebook, in tracking down anyone who worked in St Joseph's Primary School in Lisburn between 1990 and 1996.The post attracted a number of responses from the public before the police removed it from the social networking site on Wednesday.Police refused to disclose what crime they are investigating, however, it's believed the allegations centre on a woman who taught there.A PSNI spokesman also refused to comment on the post or reveal what the investigation concerned.The school said it was taken "by surprise" by the post on the page which has over 6,000 followers.It has stressed that the member of staff concerned no longer works at the school.In a statement, principal Maria Gough said: "The principal and governors of St Joseph's PS Lisburn were alerted late last night to a social media post from the PSNI public protection unit branch, regarding the school."This post caught them totally by surprise. Previously they had no official interaction with the PSNI."This morning following a conversation with the principal the PSNI made the school aware they are investigating an alleged incident in the school during the 1990s."The statement continued: "The complaint is in relation to a former member of staff."The PSNI has now removed the post from their social media site."As a matter of precaution guidance on this issue has this afternoon been issued to staff, and parents of St Joseph's PS Lisburn by the principal, in conjunction with the CCMS."The school wishes to make it clear that the individual concerned no longer works within the school, and at all times the school has cooperated fully with the PSNI on this matter."