That is why you have working theories and invalid theories.
A working theory can be proved, disproved or further modified. Where an invalid theory is exactly what is said on the tin.
So let's think about the moderator, which theories are "working" and which are "invalid"?
1) The blood was Sheila's and got in there from the killings.
2) The blood was an intimate mixture of the parents (got in there from the killings).
3) The blood was rabbit's blood.
4) The blood was Sheila's menstrual blood, planted
5) The blood was Sheila's blood, planted by the relatives which they obtained from blood in the house
6) The blood was Robert Boutflour's blood, plainted by him (or possible got in there by mistake).
7) The blood was David Boutflour's
The blood was planted by the police
