A file photo shows a puppy. The teen was high on marijuana in July 2011 when he threw a rock and injured a three-month-old Shepherd mix puppy which was being cared for by a cousin. (AFP)

WINNIPEG -- A Manitoba teen recently sentenced for battering a relative's puppy with a golf club and severing its head with a garden chisel has been convicted in a cruel attack on a mentally challenged Winnipeg man committed while out on probation last summer.

The youth, 16, was convicted after a three-day trial Friday of several charges including assault and break, enter to commit robbery relating to an odd, apparently pack-influenced crime on July 26, 2012.

The 24-year-old victim was out for a walk near Kildonan Place when he was confronted by four youths on bikes.

The accused took a lead role, produced a knife and threatened to kill the vulnerable man if he didn't hand over his iPhone, court heard.