No action will be taken against a police force which had contact with a schizophrenic man before he killed a schoolboy, the police watchdog said.
Harley Watson, 12, was hit by a car outside Debden Park High School in Loughton, Essex, on 2 December 2019.
Terence Glover, 52, was detained indefinitely under the Mental Health Act last year.
An inquest in July concluded failings by Essex Police had "possibly" contributed towards his death.
An investigation by the Independent Office for Police Conduct (IOPC) said the force "received a high volume of calls" from Glover from 2016 onwards where he "made threats to harm members of the public".
The inquest in Chelmsford heard Glover, who was diagnosed with paranoid schizophrenia, made repeated 999 calls in the months before the crash, where he said he "might run some schoolchildren over".
He was arrested in September 2019 on suspicion of making malicious communications, but following a mental health assessment - which lasted less than three minutes - he was not detained, the inquest heard.
The inquest jury said Glover had not been properly assessed and an opportunity to prevent Harley's subsequent death was missed.
Jurors concluded police had not put sufficient resources into the case, they did not pass concerns about Glover across departments and releasing Glover from custody had been a "failure".
After the inquest concluded Deputy Chief Constable Andy Prophet said: "I would like to offer my sincere apologies for the failings by Essex Police identified at the inquest.
"It goes without saying that we accept in full the findings of the inquest.
"I'm confident we have learned from this and that the changes we've made will ensure our county is even safer."
The IOPC said "there was no indication any police officer had behaved in a manner that would justify the bringing of disciplinary proceedings or had committed a criminal offence".
"We concluded Essex Police operated within the policies and procedures in place and considered options that were available to them in attempting to deal with the man," the report said.
The IOPC added that the force "had already begin to review their relevant existing policies and develop new strategies" and therefore it had "not identified any additional learning".