Termination of contract after lock in period but before period agreed and leaving without giving key

7 months ago my parents gave our house on rent to a lady. The lock in period was 6 months and the period in agreement was 11 months i.e from 14.04.2018 - 13.03.2019. But on 24.11.2018 i.e after lock in period but before the period written in agreement, she informed that she will leave the house on 1.12.2018. And when parents used to call her or text her she would not reply most of the time. She did not give the last two month rent and told to deduct it from security deposits. Now on 2.12.18 before my parents would reach she left the place and have done damage to the furniture in the house which was not written in agreement. The keys of the house were with estate agent about which my parents were not aware. So my parents went to police to open our house and gave it in writing but after two days when my parents went to police station and the estate agent was called that time my parents came to know that the keys were with the estate agent. And now police denied to accept the notice and said that they can't do anything and to give the security deposit after deducting rent of two month to the estate agent and settle the matter or else the case will go to court. Now on what basis can my parents demand the keys of our house back and not give the security deposit? As the tenant left before the period agreed, without handing over the keys and some people of society did complain about her.