A police officer places flowers at the entrance of Masjid Al Noor mosque in Christchurch, New Zealand, March 17, 2019. REUTERS/Jorge Silva

WELLINGTON (Reuters) - New Zealand’s police chief said on Monday that they are certain there was only one attacker involved in the mass shooting in Christchurch last week.

“I want to definitely state that we believe that there was only one attacker responsible for this horrendous event,” Police Commissioner Mike Bush told a media conference.

“That doesn’t mean there weren’t possibly other people in support, and that continues to form a very, very important part of our investigation,” he added.