Breaking a lease is a serious matter. However, if a tenant decides that the landlord's harassment is making the unit unlivable, the tenant may be able to move before the expiration of the lease term without liability for unpaid rent or re-rental fees. The tenant must have solid, convincing documentation outlining the type of harassment, when it occurred and who did the harassing.
Send a letter to the landlord stating this information and the intention to move because of it. The tenant should keep a copy of this letter. After moving, the tenant may have to present a defense if the landlord tries to collect unpaid rent for breaking the lease.