Were his calculations of probabilities erroneous?
No.

He had started with a positive fact, the murder.

He had discovered the particulars; his inferences were correct, and the criminal was evidently such as he had described him.

The man M.
Daburon had had arrested could not be the criminal.

His confidence in a judicial axiom had led him astray, when he pointed to Albert.
"That," thought he, "is the result of following accepted opinions and those absurd phrases, all ready to hand, which are like mile-stones along a fool's road! Left free to my own inspirations, I should have examined this case more thoroughly, I would have left nothing to chance.
The formula, 'Seek out the one whom the crime benefits' may often be as absurd as true.