LONDON — One September day in 2010, a man who said he was the former electrician of Pablo Picasso entered the Paris office of the Picasso estate, wheeling a suitcase filled with 271 of the Spaniard’s artworks.

The electrician, Pierre Le Guennec, had traveled from his home in southern France with his wife, Danielle. He said he wanted to authenticate 180 watercolor paintings, lithographs and Cubist collages, as well as two notebooks with 91 drawings.

The treasure trove had been in their garage for almost 40 years , Mr. Le Guennec said, gifts from Picasso decades earlier.

Thus began a nearly 10-year saga in which a lawsuit claimed that the artworks were “stolen goods”; the police began an investigation; the courts heard contradictory testimony; and multiple appeals and hearings took the defendants and Picasso’s heirs all the way to France’s top appeals court.