Surrey Police needs to improve how it investigates crime and tackles serious and organised crime, a government inspector has said.
A report said the force was inadequate at protecting vulnerable victims.
Surrey Police boss Nick Ephgrave said the force was good at preventing crime but this potentially came at the expense of investigations.
Inspector Zoe Billingham said Surrey showed a "commendably strong commitment to keeping people safe from harm".
'Not good enough'
She said the force had strong, mature neighbourhood police teams who worked well with councils, and neighbourhood officers had more training than in other forces.
But she said: "The way the force investigates more complex crime requiring specialist investigations is still not good enough.
"Many investigations that we reviewed were not of an acceptable standard and there were long delays in examining computers and mobile phones for evidence."
She said the force needed to improve its understanding of the threat posed by organised crime, improve its process for mapping those groups, and fully mobilise its neighbourhood teams in the fight against organised crime.
Mr Ephgrave, temporary chief constable, said the force was already tackling concerns by increasing resources to protect the vulnerable, and providing more training, better process and use of systems, and a culture change in how the force operated.
He said: "None of these things can provide an instant fix but together they are starting to deliver positive results."
A separate report by HM Inspectorate of Constabulary (HMIC) in December last year found Surrey Police's approach to protecting vulnerable people to be inadequate.
Force 'turning round'
Surrey police and crime commissioner Kevin Hurley said changes were already in place, including a change in chief constable.
This month it emerged that Mr Hurley had considered seeking Ms Owens' dismissal as Surrey Police chief. She resigned last autumn to move to her new role as director general of the National Crime Agency
Mr Hurley said: "When we look at where the buck stops, it stays with the team manager."
But he said the force was already turning around, with reductions in robbery and burglary, improvements in violent crime and rape investigations, praise for the force's action on anti-social behaviour.
The BBC has approached Ms Owens for a comment. In a previous response, she said blame apportioned to her was "ill-considered and inaccurate".
"I was selected to my current role by the Home Secretary after a lengthy and thorough process and am now focused on leading the National Crime Agency in its fight to cut serious and organised crime," she said.