Dartmouth police said they arrested a sex offender who was living behind Potter Elementary School.

According to police, the arrest happened at 5:20 a.m. on Thursday after finding 47-year-old Robert Magrath living in an encampment in the woods behind the school.

As a result, Magrath was charged with failing to register as a level 3 sex offender — the highest level possible in the state, which is considered to be a danger to the public with a high risk of reoffending.