Question

How is the intruder trapped in and handed over to the police by gerrard ?

Answer 1

when the Gerrard and intruder are going to leave the house ,Gerrard push intruder into the cupboard and locks.
that's why the intruder is handed over to the police by Gerrard

Answer 2

When the Gerrard and Intruder are going to leave the house, Gerrard push intruder into the cupboard and locks.

It is the reason that intruder is handed over to the police. He used his presence of mind and locked intruder in a cupboard.

His plan is actually good and able to arrest the intruder with the help of police and arrest him immediately.