Samantha Lee failed to make the “correct investigative inquiries” after the monster exposed himself at a McDonald’s on February 27, 2021.
Just three days later, Couzens kidnapped, raped then murdered 33-year-old Sarah after flashing his Met Police ID.
Lee, who left the force for an OnlyFans career, has now been found guilty of gross misconduct following a disciplinary hearing.
The flashing incident in Swanley, Kent, was reported to the police by a horrified fast food worker on February 28.
Couzens had previously exposed himself to another employee at the same drive-thru on February 14, 2021.
Staff had taken a registration number and a black Seat was identified as belonging to Couzens.
A credit card in his name was used to pay while ANPR and cell site data was used to track his car in the area at the time.
Despite this, the CCTV footage was not reviewed and no enquiries were made regarding Couzens’ Mastercard number.
Lee – based in the South Area Command Unit – was the first person on the scene on March 3 – the day Sarah was kidnapped.
But she failed to “diligently exercise her duty and responsibilities”, a disciplinary hearing in London was previously told.
The ex-cop also lied about her actions when questioned – claiming she believed the CCTV deleted automatically.
She was actually told by the manager Sam Taylor that while the drive-through CCTV deletes automatically, other CCTV footage showed Couzens’ car.
In a report made after attending the restaurant, Lee recommended that Couzens be arrested and questioned.
Paul Ozin KC, prosecuting, said she claimed she believed the report would be allocated to a different team to follow up on.
But she did not put the witness statements and the receipts in a sealed evidence bag – instead keeping them in a pocket in her body armour.
Mr Ozin said: “One of the central issues of this case is whether there has been some horrible misunderstanding.”
The hearing was told she deliberately gave a “false explanation in the course of the misconduct investigation that followed for why she failed to secure relevant CCTV footage”.
Mr Ozin added: “She was more intent in getting away quickly than performing her duty properly.
“Is it an unpalatable conclusion that PC Lee didn’t bother to get the CCTV and was relying on others to do that for her.
“She’d later lied to others when she knew that mistakes she had made escalated astronomically.
“She spent 15 to 20 minutes at the scene when an hour had been allocated.
“In particular she didn’t obtain local CCTV.
“This is not a case in a vacuum, there were other important facts that were known about. She knew the same driver had used the MasterCard twice. It was self-evident that the card still worked and there was no suggestion that the car or card had been stolen.
“PC Lee does not suggest in any of her later accounts that she took any effort to investigate.”
On her Officer Naughty website, Lee calls herself a “29 year old , curvy Ex-Metropolitan Police Officer who is now a spicy online content creator”.
She adds: “I served in the Metropolitan Police Service for nearly 7 years! I made plenty of memories some good, some bad and some really sad.
“I made a choice to leave and start my own business as an adult content creator for many reasons which some may or may not have heard about.
“It’s been the best decision I’ve made for my mental health and my happiness. Life’s too short and we all deserve to know happiness!”
Couzens, 49, pleaded guilty in February this year to three counts of indecent exposure.
The charges took place on November 13, 2020, February 14, 2021 and February 27, 2021.
Couzens, who worked in the parliamentary and diplomatic protection command – murdered Sarah, 33, days later on March 3, 2021.
During the first incident, the fiend performed a sex act on himself while naked as a woman cycled past him in woodland in Deal, Kent.
Couzens, who is serving a whole life jail term for Sarah’s kidnap, rape and murder, was handed a 19-month sentence.