The files were dumped at Farrington Moss recycling centre
Sensitive legal documents relating to a major drugs prosecution in Liverpool have been found on a tip in Lancashire.
The files, which were meant to be destroyed, relate to Operation Montrose, which saw 59 men jailed over drug dealing in 2005.
They include more than 100 "restricted" statements from officers and forensic experts and the personal details of witnesses and suspects.
HM Courts Service (HMCS) said it was investigating.
A spokesperson said: "We will investigate all allegations of breaches or incidents.
"HMCS takes data security extremely seriously."
The files had been dumped at Farrington Moss recycling centre near Preston.
They were found by a member of the public who noticed the huge pile of files while he was recycling his newspapers.
The CPS said copies of its files were sent to lawyers and the courts.
It said it was "highly unlikely" that the files that were found were the original CPS documents.
Assistant Chief Constable Colin Matthews said he was calling for an urgent review of procedure.
"This is of particular concern due to the sensitive nature of some of the documents recovered," he said.
"During a court case, documents are supplied to the Crown Prosecution Service, the courts and defence and as such Merseyside Police has no control over how other parties dispose of their copies."
He said that inquiries were continuing as to how the files ended up on the tip but they were confident they were not put there by Merseyside police.
"I will be calling for an urgent review of the procedures for the distribution and disposal of court papers to ensure that the safety of witnesses is not the subject of potential compromise in the future," ACC Matthews said.
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