Scenes of crime officer Stephen Beattie worked for Northumbria, Staffordshire and Cleveland forces before being suspended in 2011 and later resigning.
More than 350 of his cases, including suspicious deaths and arsons, have been reviewed.
The Crown Prosecution Service has said no criminal charges will be brought.
Both Cleveland Police, which Mr Beattie joined in 2002, and Staffordshire, where he had worked since 1996, investigated him with the Independent Police Complaints Commission (IPCC) managing the inquiries.
The reports have now confirmed Mr Beattie:
But the reports concluded that none of his actions significantly impacted the results of his investigations.
IPCC commissioner Cindy Butts said: "Stephen Beattie repeatedly lied about his qualifications and made judgements in cases that were both outside his remit and his level of expertise.
"Cleveland Police and Staffordshire Police have conducted meticulous investigations examining hundreds of cases and we know that, thankfully, his poor performance did not have a significant impact on the cases he was involved in."
Mr Beattie did receive an official caution in relation to a fraud offence.
Cleveland Police concluded that if he was still employed he would have a case to answer for gross misconduct while Staffordshire concluded he would have a case to answer for misconduct.

Shares in miners rebounded as investors looked for bargains following recent falls in the sector.
Sentiment was also helped by upbeat economic data from China - the world's largest importer of raw materials.
BHP Billiton rose 3.3% and Rio Tinto was 3% higher. The two firms topped the FTSE 100's risers board, with the index up 28.67 points at 6,715.24.
Shares in the London Stock Exchange rose 2.2% after it reported a 16% rise in half-year operating profits to Â£239.4m.
The group's results were boosted by the contribution from the US Frank Russell business, which it bought last year and combined with its own FTSE index business.
Legal & General shares rose 1.8% after the insurer reported an 18% rise in operating profits to Â£750m in the first half of the year.
Ryanair shares were up 1.6% after the company said that in July it became the first airline to carry more than 10 million passengers in a month.
Ryanair said it carried 10.1 million customers last month, up 11% from a year earlier.
On the currency markets, the pound rose 1.6% against the dollar to $1.5589, and climbed 0.3% against the euro to â‚¬1.4350.

Bates, who has been Tigers promoter for three years, has taken full control of the Lions and will work alongside co-promoter David Darcy.
Bates said: "We're only weeks away from the new season and so our main priority is to quickly form a team.
"We have opened talks with several riders and should be in a position to announce the first signings any day."
Lions endured a miserable season last time out and finished bottom of the Elite League table.
But Bates said he hoped the club's financial difficulties were a thing of the past.
"I am aware that Leicester went through a difficult trading period last season," he said.
"And I will be doing everything possible to ensure that the club is placed on a sound financial footing that secures the future of Leicester Speedway for years to come."
A police employee lied about his qualifications, mishandled evidence and was generally poor at investigations, two reports have found.
[NEXT_CONCEPT]
(Noon): The market remained in positive territory during lunchtime trade, with mining shares among the top risers.
[NEXT_CONCEPT]
Leicester Lions Speedway have been bought by Sheffield Tigers promoter Damien Bates.