(WFLA/CNN Newsource) – A teacher in Massachusetts was arrested Thursday after allegedly leaving live ammunition in school in an effort to make a point.

Police say Alfred Purcell III told the staff he found a live round of ammunition in a stairwell at Southbridge High School.

The building was immediately placed on lockdown.

Police say security video later showed that Purcell himself planted the bullet.

Investigators say he did it to prove the school needs to install metal detectors. 

Purcell is now facing multiple charges, including two counts of carrying ammunition of school grounds.