We completed the rehab work on 10/5. The basement bathroom was hooked to water on 10/3. No water issues. The Realtor was on the property on 10/6 to take pictures, the electronic lock was installed on 10/7. Then we have the first showing on 10/11 when my relator called me for flooded basement. I was out of town for the weekend so I asked to shut off water main.

I got back on Sunday 10/12 and drove straight to property. The finished basement is flooded. I could not find any leaks until I opened the bathroom vanity door. The supply line compression nut is opened half way thru. The water is coming from there. I tighten the nut, the water leakage stopped. 

Now I am confused, Is it just a bad luck or some one tried to damage the property?

As I said the line was installed on Friday and No water was noticed on Monday.

As per my Realtor, the house went on MLS on Wednesday night, and the first showing was on Saturday.

We have to cancel two more showing this week because of the mess.

Who would have had access between 10-7 and 10-11, and what would be their motive?  Likely it was loose from day one, and "let go" later.  Obviously, the electronic lock would show if anyone used it to access the property before 10-11.