In a group, postdoc A believes postdoc B sabotaged her experiments. A shares her frustration with the PI (without proof) in a "half-jokingly, half-serious" sense. Since then, strange things appear to be happening in the lab -- specifically, B's experiments are behaving strangely. There has been a serious decline in trust between A and B.
How should the two postdocs proceed? Should they meet? Should the PI mediate between the two? Should the PI talk to them separately? Or together?
Ultimately, how should the PI address the problem, knowing that an investigation is in practice impossible and with the goal of reestablishing a minimum level of mutual trust?
EDIT: Pushed by the PI, the 3 actors openly talked about these issues, agreeing that sabotage is extremely serious, but without pointing the finger to anyone. That seems to have released quite a lot of pressure and helped to normalized the situation. Hopefully it will last.