Bowman said police were working with one school "at the moment" in the area.
"That's really important, the children of that school will be extremely traumatised."
"This is a tragic, tragic event involving an eight-year-old child, you only have to use your own imagination to know the trauma they [the family] are going through at this difficult time."
Several police personnel from Western Southland and Dunedin were involved in the arrest, he said.
Given the matter was before the Youth Court, Bowman said he could not comment in detail.
"This is a truly tragic incident and our thoughts are with the family of the child at this difficult time.
"Police, along with Victim Support, will continue to support them and the tight-knit Otautau community throughout the investigation.
"Police are not seeking anyone else in relation to the incident and wish to reassure members of the public this was an isolated incident."
Environmental Science and Research (ESR) scientists were involved in forensic examinations at two houses, which would take at least two days, he said.
There was a hive of police activity in Otautau late last night - around 11pm, after police were called to the area about 10.30pm.
Family friend Karl Jackson said the boy's father rang him last night with the news of his son's death.
"He didn't know what to say last night, he just broke down...he will never be the same."
He said the family were not new to the area, but had just moved to a new house in Otautau a week ago.
The boy was gifted at arts and crafts, he said, and was a "brainy kid".
"All his mates will be in mourning... he touched every heart that he saw."
Otautau Gallery owner Pamela Hopkins said the community was "shattered".
She said when she heard sirens last night she did not believe it would be "something like this".
Otautau was a small and close community where everybody knew each other and where people felt safe.
No-one expected "something like this would happen here".
"It is heartbreaking."
"Because my gallery is in the main road, I have a lot of locals coming here and I have a good feel of [what] this little town is like.
"I'm used to see this kids walking around, riding their bikes - feeling perfectly safe.
A reporter at the scene this morning said about six houses were inside a police cordon in Eton St and one in neighbouring Rye St.
She could see three police cars next to the cordon and a police officer was asking people who entered Eton St for details, including name and address.
Southland Mayor Gary Tong this morning said the community was in shock.
Tong, a former police officer, said the rural town of about 700 was a tight-knit group.
"It'll be traumatic for the community. I don't know the full details at this stage but hearts and thoughts are with the families and those that attended the incident as well - they're all volunteers in that area."
Two properties remained under police guard early this morning, police said.
A southern fire communications spokeswoman said they were called to a "medical response'' in the area last night, but referred all other inquiries to police.
Police are appealing for anyone with any information to contact authorities immediately:
- Invercargill Central Police on: (03) 211 0400, the non-emergency police hotline 10-5 or anonymously via CrimeStoppers: 0800 555 111.
- additional reporting RNZ
