 Why are the police willing to risk the life of Gerri to kill Lane?
Raging , Trooper Lane hovered three thousand feet above Tammany Square. The humming paragrav-paks embedded beneath his shoulder blades held him motionless above Newyork's three administrative towers. Two black paragrav-boats whirred along the translucent underside of Newyork's anti-missile force-shield, the Shell. Lane dropped lightly to the floor, inside the room, in battle-crouch. Two policemen were killed, four others seriously injured. Lane is an insane killer. Lane's mailed hand snapped open a pouch at his belt. The force-bomb "exploded"—swelled or inflated, really, but with the speed of a blast. It shaded the view from his window and re-entered the tower wall just below.
 Lane is too dangerous to be left alive. They can't risk him escaping just so they can rescue Gerri.
 Lane is too dangerous to be left alive. They can't risk him escaping just so they can rescue Gerri.  They think Lane may be infected with a biological weapon.  The police don't care if they kill Martians.  They don't believe that Gerri is in the room with Lane.