For info, from the Germanwings accident report....
...... some of the previous events listed in (previously in the report , "ed" ) show that even with two persons in the cockpit (i.e. two pilots), a suicide remains possible. This “2-person in the cockpit” rule cannot fully mitigate the risk of suicide, although it is likely to make it more difficult. In addition, this rule may introduce new security risks by allowing an additional person inside the flight deck. Consequently, the BEA acknowledges the potential safety benefits of the “2-person in the cockpit” rule, although the security risks and training needs for the staff performing the tasks of that second person have to be carefully assessed.
(My emphasis).