It is none other than Martin Caidin who, in one of his more extreme flights of fancy, had a P-38, still in US national markings, stalking stragglers to shoot them down, only eventually to be entrapped by a YB 40. The origins of Caidin's story, his "research", lies in a novel by Glenn Infield. A novel, a work of fiction!
Happily, despite Caidin's fancy, which has developed a life of its own in cyberspace, there is a foundation of truth to the story.
There was a P-38 captured and flown by the Italians. It had landed by mistake on Sardinia on 12th June 1943 after a navigational error by its ferry pilot. The US national markings were over painted in a dark olive colour (probably Verde Olivia Scuro) and white bands applied on the booms. White "sabaudian" crosses were applied to the fins. There are photos of this aircraft online.
August 11, 1943 Col. Angelo Tondi (not Caidin's Guido Rossi, who may have been a character in the novel for all I know) shot down a B-17F serial 42-30307 of 419th BS, 301st BG of the Italian coast in this aircraft. This was the only success for this aircraft and it was the only P-38 the Italians flew against the USAAF.
Cheers
Steve