Verdict reserved in WA cop's assault trial

A magistrate has reserved his decision in the trial of a policeman accused of grabbing a homeless man by the throat and "slamming" him to the ground during a strip search at a Perth lock-up.

Sergeant Lachlan Nairn Boath has been on trial this week in Perth Magistrates Court accused of assaulting Clinton Nicholson in June 2012 at the city's watch house where he was the officer in charge.

Mr Nicholson testified that he was a homeless drug user at the time and admitted being "a little mouthy" at police before he was "charged" by Boath and left gasping for breath.

The magistrate has reserved his decision until July 24.