Eviction of occupier

We bought a property 2 years ago, and a small portion of the building is occupied by a person. He was never legal tenant, and never paid any rent to the previous owner or tried to pay rent to us. Recently he took new electric connection by producing a forged lease agreement and we objected to WBSEDCL. After filing RTI we got hold in the said forged agreement and after inspection, we found out the lease agreement is not only forged, it's also full of mistake. The agreement is on a 10 rupee stamp and signed by the father of previous owner (Who has never owned the place), the agreement only mentions a municipal holding number (which does not belong to the premise) as an identifier of the premise. In the forged agreement rent is set to Rs. 100/month which he never paid to any of the previous owner or us. Said agreement also does not have any witness, and it is not registered, notarized. We contacted the previous owner and he confirmed that the agreement in question is forged, and he/his father never had any agreement with said occupier. Previous owner allowed the occupier to stay in a small section of the premise (~50sqft) out of goodwill. What can be done at this situation to evict the occupier?