Which molecule in the krebs cycle do you believe can only be created by living organisms?
Acetyl coenzyme A would probably be a fair guess. Although alpha ketoglutarate would be another one.
And, please, don't try and argue that because we can synthesize it in a laboratory, it just happened to naturally form in a prebiotic sea somewhere, unless you are prepared to try and convince me that the pre-biotic oceans contained such substances as Adenosine 5'-Monophosphate, Pyrophosphate, Adenosine 5'-Triphosphate, Monobasic Potassium Phosphate (etc, etc,) all in the right molar concentrations as well as just the right concentration of buffer reagent for the reactions to occur as well as the correct amounts of Mangesium Chloride, Ferric Chloride, etc. etc. etc.
The whole "we find organic chemicals on Titan, therefore life can arise abiotically" falls on its face when you take the time to look at the actual chemicals involved in life.