Updated

Prosecutors say the son-in-law and daughter of a real-estate heiress shot to death outside a hospital in southern France are among 23 people being held in the investigation.

Helene Pastor, whose family built a real estate empire in Monaco with wealth rivaling that of the royal family, was shot May 6 after visiting her son in a hospital in Nice. Pastor and her chauffer died some days later. The attackers fled.

Marseille prosecutor Brice Robin said Tuesday that Pastor's daughter, Sylvia, and her husband, Wojciech Janowski, Monaco's honorary Polish consul, were detained after a painstaking investigation that involved surveillance video from Marseille and Nice, as well as DNA material and financial records. Robin said two men believed to have carried out the shooting were also among those held.