Mr Sawyer said a firearm – described by witnesses as a pump action shotgun – was recovered from the scene.
He added: “Multiple shots have been fired from a firearm during that six-minute-or-so period.
“There are some 13 scenes and potentially more scenes.
“There are therefore five people of Plymouth who have lost their lives overnight – and Mr Davison himself – including a particularly young child.”
The incident, the first mass shooting in the UK for 11 years, was not being treated as terror-related.
Witnesses claimed the man had “gone berserk” before opening fire.
Videos circulating on social media on Thursday night appeared to show a bloodstained body lying on the pavement under a white sheet.
Who is the gunman?
The suspect was named locally on Thursday night as Jake Davison.
The suspected killer, 22, described being “defeated by life” in videos recorded just weeks before the massacre, as he blamed his troubles on not having a girlfriend.
A gun obsession was also apparent from a playlist of videos he had compiled.
He had received treatment as an adolescent for mental health issues, The Times reported.
In his final video blog, on July 28, the suspected killer spends 11 minutes ranting about how his life has hit a dead end, as he struggles to attract women or lose weight.
“I’m beaten down and defeated by f—— life, that drive I once had, that’s gone,” he says.
At the climax of his final video blog, Davison claims he likes to think “I’m a Terminator”.