McArthur appeared in the Hamilton District Court for sentencing on Monday when he was jailed for 22 months by Judge Denise Clark.
Burroughs told the Herald the staff member saw a black object in his client's bag and thought it was a gun.
He said the 33-year-old was originally charged with aggravated robbery but the charge was reduced to robbery after police accepted he didn't have a gun - one wasn't found on him at the scene.
Burroughs said although his client had amassed a large number of convictions - 65 - he also had a mental health problem that he was struggling to get help with.
He lamented the system and said more should be done to help ensure those suffering from mental illnesses received follow up care.
Instead, once they finished their prison sentences they were often just kicked out the door with a wad of cash and in no time, resulting in a "revolving door" of crime and prison stints.
"That's why we've got so much recidivism in this country."
His client was not only diagnosed with schizophrenia but also epilepsy and diabetes. Most recently, he was diagnosed with an anti social disorder.
If they didn't receive follow up support there was no way of ensuring their medication was being taken properly.
"If they take it, they take it with out things which gets way out of control and then they become a danger to the rest of us."
He said prisoners should be upskilled during their time behind bars, rather than just left spending "time in the gym".
However, he praised Judge Clark for imposing release conditions, which his client was prepared to follow, that included that he take any medication prescribed to him by his treatment team, not to possess or consume drugs that have not been prescribed to him.
The crime also clocked up a second strike which meant he serves his full sentence with no parole.