California police turn to decoys & undercover agents to trap person shooting at Apple & Google buses

The FBI is also involved, and local police are putting undercover officers on the real shuttles, the CHP's John Fransen told Business Insider. Those people will "take appropriate action" if a bus is shot at, Fransen said, though he declined to explain what that might entail.

The charter bus operator, Storer, is further incentivizing capture by offering a $10,000 reward for information leading to an arrest.

Since January, there have been 20 or more shootings at charter buses in the San Francisco Bay Area, among them five used by Apple and Google workers. Apple decided to start re-routing shuttles as a safety precaution, even while it was still unclear whether guns were involved.

The weapons used have been shattering glass and causing dents, but without any injuries.

One possibility is that resentment against tech industry shuttles has come to a boiling point. Residents have accused the buses of driving up already high rents along their routes, since engineers with companies like Apple, Google, and Facebook often command large salaries and are willing to relocate for the convenience.

At the same time, the buses could simply be an easy target for people wanting to take potshots or sow chaos, which may make investigations that much more difficult.