When is a property "officially" reserved for tenant?

[Charlie Gruber]

I have prospective tenant who has signed a lease but hasn't sent deposit yet.  I made the mistake of also signing lease and sending back to them before getting deposit (won't make this mistake again!)

I now have someone else ready to give me a check and sign lease today.  What is my legal/ethical obligation to first people that signed lease but no deposit yet.  In my mind until have both signed lease AND deposit property isn't reserved but feels like I'm in gray area since I've signed lease.

Not sure if it matters but I'm in Colorado.  Thanks in advance for help.