https://en.wikipedia.org/wiki/Principal_investigator

In many countries, the term principal investigator (PI) refers to the holder of an independent grant and the lead researcher for the grant project, usually in the sciences, such as a laboratory study or a clinical trial. The phrase is also often used as a synonym for "head of the laboratory" or "research group leader". While the expression is common in the sciences, it is used widely for the person or persons who make final decisions and supervise funding and expenditures on a given research project.

after the Great Science Cockup of '89 all scientists are overseen by a noir-style private investigator, the whiskey and cigar costs are high but they have solved ~8 murders per year since

PI = principal investigator, or the leader of the lab. Also known as the professor. The closest comparison to regular jobs would be that the PI is the manager. They typically no longer do actual lab work and typically fulfill a role that is entirely managerial, so they're often removed from and therefore entirely oblivious to goings-on of the lab. It's a somewhat common occurrence for lab members to have a concern that the PI dismisses because they're unaware of the severity of the concern, or for the PI to have a concern that lab members have already addressed