AN undercover US cop who nailed the sex fiend plotting to kidnap and murder Holly Willoughby has told for the first time how smashing the case marked “a good day”. In an interview with The Sun on Sunday, the officer revealed he was unaware of the TV star’s fame when he rumbled security guard Gavin Plumb’s sick plan to kill her. But he quickly pieced together her identity and enough evidence to inform the FBI of the deadly scheme — and snare the “dangerous” man behind it.

It came as the detective, who cannot be named due to the nature of his work, was hailed by law enforcement chiefs for his “brilliant” sleuthing skills after he caught Plumb conspiring to snatch Holly in an on-line chatroom called “Abduct lovers”. As the obese loner, 37, was ­sentenced to life behind bars for his horrifying crime on Friday , the cop — who used the alias David Nelson in court — said: “Any time we can ­identify, disrupt and destroy a plot is a good day. “Early on in the investigation, Plumb had identified Ms Willoughby by name.

Open source information was obtained and we were initially unaware of her job and position within the media.” Mum of three Holly, 43, quit ITV’s This Morning last October when the plot came to light. A jury at Chelmsford Crown Court heard the impact of the vile threats on the TV beauty had been “life-changing”.

Owatonna police chief Jeff Mundale has praised his undercover officer for the role he played in “saving lives and prevent.