The ABC of policing literally goes: Assume nothing, Believe no-one, Check everything. - Ben Aaronovitch

A lot of people have died in the Underground, through accidents, stupidity, or suicide. All the one-unders who'

“When you say shades, what do you mean?” I asked. “Do you mean Fae?”
“I mean everything that’s not normal,” said Mrs. Chin.
“Like New Jersey,” said Stephen.

“That’s assuming that the Singularity hasn’t already happened,” said Victor. “And we’re not sentient virtual personalities inhabiting a simulation of reality.”
“How would we know?” I said.