Take the primary effect as being the child disappearing from her room.
St Thomas Aquinas teaches us that every effect has at least two causes, he also implies that causes may be condition or action. So the basic principles ain’t exactly some new kind of Voodoo man.
Any theory must accommodate the available known evidence*.
*“the available body of facts or information indicating whether a belief or proposition is true or valid”.
Note facts not speculation.
Method:
1 Define the primary effect.
2 Determine the known causal relationships including the actions and conditions of each subsidiary effect.
3 Show the causal relationships to including specific action and conditional causes.
4 Show evidence to support the existence of each cause.
5 Determine if each set of causes is sufficient and necessary to cause the effect.
For there to have been an abduction the paths of the child and abductor must cross so either the child vacated the apartment or the abductor gained access to the apartment. Using known evidence show how either was possible.
I wouldn't comprehend anything Thomas Aquinas said but I do follow your line "For there to have been an abduction the paths of the child and abductor must cross so either the child vacated the apartment or the abductor gained access to the apartment. Using known evidence show how either was possible."
Known evidence:
For the " the child vacated the apartment" abduction theory.
1. it is dark and there is space and cover so an abductor could observe the McCann apartment without being seen.
2. if the child came to him as in a woke and wander situation he doesn't need to enter the apartment (evidence -no sign of forced entry)
3. The tapas 8 (9-1) thought she is closeby and search the immediate areas without success. (Evidence in the statements)
4. Man seen carrying child by the Smith family (all Tapas 9 are accounted for so not one of them) Potential abductor.