Stockholm and Region South are the worst performing regions.
"We can turn it around," Dan Eliasson tells newspaper Dagens Nyheter.
The ability of the police to investigate crimes has been sharply criticised since the national reorganisation when the 23 police authorities were merged into one central body.
The police officers union has complained that its officers are expected to do too much, have low pay and low morale, resulting in an increase in people leaving the profession.
In August, Home Affairs minister Anders Ygeman, (Social Democrat), announced that performance had to improve.
Statistics from Dagens Nyheter show that results are worse than ever.
Between January and October 2016, a total of 120,015 investigations were taken to prosecution, compared to 131,890 for the same period last year. A drop of 9 percent, which DN says has continued into October with even worse results.
"Up to October this year we have not received the turnaround we wanted. This is something we are working incredibly hard with. It is not enough, we must take further action. It will turn," said national police chief Dan Eliasson to DN.