How to Evict A Problem Tenant?

[Philip Coiro]

Hello BP! My neighbor is a senior citizen woman who has a long time tenant in the mother/daughter type of apartment here in Nassau County, Long Island, NY. This is an illegal appartment, not in that it's built improperly but that the village and city require permits to have apartments etc...

This guy has been there for many years, has always paid but is very under market value. When she requested small increases over the years he would yell at her and threaten to go to the town. Now she is noticing dead insects on the windows, not one or two, but quite a lot. She went down there to check out the place at it's as you would imagine a complete disaster. 

She obviously has no written lease, what are her options to get rid of him?