What to do when tenant breaks lease the day before moving in

[Charlotte Raycraft]

Hi Everybody, I am wondering if anyone knows the rules in Colorado when a tenant breaks a lease the day before moving in. The prospective tenants viewed the property and decided they wanted to rent it. They had good references and had been in the current rental for 11 years. I collected their security deposit when they signed the lease three weeks before they were to move in. We agreed the first and last months rent would be due when they moved in. First, last and security is standard in the mountains. The day before they were to move in I met them at the property to collect the rent and give them the keys and they said they didn't want it anymore as they had found a place closer to their work. Now of course they want their security deposit back immediately. Does anyone know if I can keep part of their deposit for the missed rent? I am showing the house this weekend so hopefully it will only be vacant for 2 weeks. Thank you in advance for your help. Charlotte