Holding personal tools for collateral

My boyfriend is not licensed and the people knew that when hiring him to finish their basement. They had a contract set up with phases of work. The homeowners kept forcing him to start a new phase before an older one was complete. He was leaving his tools at the job so he would not have to transport them back and forth which was fine with the homeowners. He left one night to return the next day and the homeowner called him that night and told him not to return. He requested to come and retrieve his tools, they kept telling him NO. He has called the local police department to see if they would help and they told him that its up to the officer on scene whether the officer will enforce them to return the tools or not. Now he has received a letter from the homeowner stating that if he does not give them a list of items they came up with that they would liquidate his tools. The list they gave him does not comply with the contract. The contract is not itemized as far as what items are needed to complete the phases. Can they do that? How can he get his tools back? They have a new contractor finishing the job who is also not licensed nor have they had any of the electrical and plumbing inspected. They are doing all this under the radar.

By the way this has all taken place in Maryland.

Thank you for any advise of information.