Mr Kelly has Fragile X syndrome and an intellectual disability, and walking up to five kilometres a day was one of the few things he could enjoy in life.
Then a vicious and brutal assault, unprovoked and committed by a stranger, robbed him of that in June 2020.
His attacker, 37-year-old Trevor Van Kempen, is now facing a lengthy prison term over the brutal beating.
"Mr Van Kempen has robbed Mr Kelly of almost every one of his limited enjoyments in life," County Court Judge Greg Lyon said on Tuesday.
Mr Kelly, then 45, was on his weekly walk home from a Warrnambool milk bar when Van Kempen came up from behind and punched the back of his head.
He moved in front of Mr Kelly and punched him in the face, knocking him to the ground.
While his victim was flat on his back on the ground Van Kempen was seen by a driver repeatedly kicking Mr Kelly, punching his face with both fists and jumping on his head half a dozen times.
An off-duty policeman found him nearby. Mr Van Kempen said he was "sorry I did this".
Mr Kelly spent weeks in hospital in Melbourne, requiring multiple life-saving procedures including a craniotomy to relieve pressure on his brain.
His siblings said their brother had always been truly vulnerable and the after-effects of the assault had been devastating.
"We have grieved and said goodbye to the old Matt," his brother said.
"(Now) we celebrate this perfectly imperfect human we proudly call our brother."
Van Kempen's lawyer Sally Buckley said her client was impaired at the time of the assault and experiencing a heightened state of paranoia relating to an earlier serious assault on him.
She described physical and verbal assaults by his stepfather during his childhood, and the upheaval of moving back and forward between Warrnambool and Perth while growing up.
But Judge Lyon reiterated that Mr Kelly hadn't even raised a hand in self-defence.
"In my sentencing remarks I will be acknowledging the vicious, unprovoked nature of this attack and the sustained and brutal injury that Mr Van Kempen inflicted when Mr Kelly was lying incapacitated on the ground," he said.
Van Kempen will be sentenced at a later date.
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