The M&A Lawyer, a Custody Fight and French Insider-Trading Raids

Mondays are never easy. But there’s one Monday morning Patrick Jaïs has been trying to erase from his memory -- or at least from legal existence -- for half a decade.

On a sunny morning in March 2014, French investigators stormed his Neuilly-sur-Seine home west of Paris. The officers rifled through his and his wife’s mobile phones as well as his personal laptop in a raid meant to shed light on insider-trading suspicions linked to a longtime friend’s activities.

Right about the same time, another group of investigators turned up at the Paris law firm just off the Champs-Elysees where ...