Police investigating the killing of Monaco heiress Helene Pastor last month have detained 23 people in France, including her daughter and son-in-law.
Ms Pastor, from one of Monaco's richest families, was ambushed by a man armed with a shotgun as she left hospital in the French city of Nice.
Her chauffeur also died of his wounds.
Sylvia Pastor and her husband, Poland's honorary consul to Monaco Wojciech Janowski, were among those detained in Nice, Marseille and Rennes.
Mr Janowski's bank account had seen suspicious financial flows which needed explanation, Marseille prosecutor Brice Robin told reporters on Tuesday. There were also apparent links with two intermediaries who had been in direct contact with two suspects in the shooting.
The two men were traced after police studied DNA evidence and CCTV footage from the area on 6 May, he said. The pair were described as aged 24 and 31, originally from the Comoros islands, and having a string of criminal convictions.
Video from railway stations and elsewhere showed that the two men had taken a train from Marseille to Nice on the afternoon of the shooting, gone to a hotel, and then made their way to the scene of the shooting, he said. French media had earlier reported they had spent 500 euros (£400; $680) on a taxi back to Marseille afterwards.
The shots from the sawn-off shotgun were fired through the window of the car, hitting Helene Pastor in the face and throat. She eventually died on 21 May.
Her father, Gildo, became one of Monaco's wealthiest men when Prince Rainier gave him permission in 1966 to build high-rise buildings along the sea front, AFP news agency reports. Prince Albert II attended her funeral.
Helene Pastor rarely left her luxury home in Monaco and had just visited her son in hospital when she was shot, reports say. Her income was derived from owning several prestige properties.
The family's lawyer in Paris refused to comment on the arrest of her daughter and son-in-law.