7. Under Art. 8 of the Swiss Civil Code (CC), unless the law provides otherwise, each
party must prove the facts upon which it is relying to invoke a right, thereby implying
that the case must be decided against the party that fails to adduce such evidence. A
valid contestation of facts needs to be specific, i.e. it must be directed and attributable
to an individual fact submitted by the party bearing the burden of proof. According to
the doctrine, the threshold for meeting such an obligation to specify the contestation
is – under normal circumstances – rather low, since it must be avoided that the
prerequisites for contesting an allegation result in a reversal of the burden of proof.
Nevertheless, there are exceptions to this low threshold. The exceptions concern cases
in which a party is faced with a serious difficulty in discharging its burden of proof
(“état de nécessité en matière de preuve”, “Beweisnotstand”. This is the case
whenever a party needs to prove “negative facts”. In this respect, the Swiss Federal
Tribunal makes it clear that difficulties in proving “negative facts” result in a duty of
cooperation of the contesting party who must cooperate in the investigation and
clarification of the facts of the case. However, the above difficulties do not lead to a re-
allocation of the risk if a specific fact cannot be established. Instead, this risk will
always remain with the party having the burden of proof.
8. The athlete can only succeed in discharging his burden of proof by proving that (1) in
his particular case meat contamination was possible and that (2) other sources from
which the Prohibited Substance may have entered his body either do not exist or are
less likely. The latter involve a form of negative fact that is difficult to prove for the
athlete and which requires the cooperation of the Appellants. Thus, it is only if the
theory put forward by the Athlete is deemed the most likely to have occurred among
several scenarios, or if it is the only possible scenario, that the Athlete shall be
considered to have established on a balance of probability how the substance entered
his system, since in such situations the scenario he is invoking will have met the
necessary 51% chance of it having occurred.