UnitedHealthcare CEO shooting: Search for gunman continues [Video]

NEW YORK — Police don’t know who he is, where he is, or why he did it.

As the frustrating search for UnitedHealthcare CEO Brian Thompson’s killer got underway for a fifth day Sunday, investigators reckoned with a tantalizing contradiction: They have troves of evidence, but the shooter remains an enigma.

One conclusion they are confident of, however: It was a targeted attack, not a random one.

They know he ambushed Thompson at 6:44 a.m. Wednesday as the executive arrived at the Hilton for his company’s annual investor conference, using a 9 mm pistol that resembled the guns farmers use to put down animals without causing a loud noise. They know ammunition found near Thompson’s body bore the words “delay,” “deny” and “depose,” mimicking a phrase used by insurance industry critics.

The fact that the shooter knew UnitedHealthcare …