The man is currently recovering in Waikato Hospital's high dependency unit and is in a moderate condition.
Grace said it was too early to say if gangs were involved.
She wanted to reassure the community that there was no need for concern following the incident.
"The fact an innocent member of the public was accidentally caught up in this incident is upsetting.
"This kind of behaviour is simply not acceptable and we are determined to find those responsible."
The shooting is the sixth serious incident in the Waikato in the last two months, which has seen four people left dead, and several others battling serious injuries.
"We are concerned that there have been a number of serious incidents involving people being harmed across Waikato in recent months.
"At this point in time, there is nothing to suggest these incidents are connected.
"Investigations like this are complex and can take time, however we want people to know that we are taking this seriously and are confident we will hold people to account.
"We are still in the very early stages of this investigation but the public should be assured that we will tell them anything they need to know."
Three men, at least one armed with a firearm, beat up an innocent man before heading next door and repeatedly shooting their victim.
Neighbours of the Derby St, Hamilton, house today told the Herald the gunmen first went to the wrong property in their search for the shooting victim, Mike Bell.
The innocent neighbour was in his garage drinking beer at the time when he was confronted by the gunmen about 10.25pm last night.
After a tussle, which another neighbour said saw the innocent victim get kicked, the trio went next door and opened fire on Bell.
The number of shots heard being fired ranged from three to five, witnesses spoken to by the Herald said this morning.
One woman said she heard someone - who she later found out was Bell - shout "gun" as she and her family were about to go to bed.
She then looked out the window and saw the shooting victim with ambulance staff, walking down the street and holding his arm.
Bell was a nice guy and wasn't connected to a gang, the neighbour said.
Another said the neighbour was involved in the tussle with the gunmen initially, had been drinking beer in his shed when two men armed with guns walked in.
A third man, believed to be unarmed, waited outside as they confronted the man.
He said the victim was doing okay but was more worried about his children who were inside his house at the time.
Violence in the Waikato
• September 19: Michael Bell seriously injured after being shot in his Nawton, Hamilton, home. Offenders still being sought.
• September 14: 17-year-old shot in face in north Hamilton suburb of Horsham Downs. Offenders still being sought.
• August 31: Leigh Wallace shot dead in an alleged domestic incident. Arrest made.
• July 13: Mitchell Paterson, 26, found dead in the water beneath McLaren Falls bridge near Tauranga. Multiple arrests made.
• July 8: Hamilton man Robert Nelson shot dead in the Melville home of his girlfriend, Kahlee Marshall, who was also shot and injured. A third man, 17, is recovering after being shot four times. Offenders still being sought.
• July 4: Huntly man Wayne Noda found dead in his home. Offenders still being sought.