PARIS — The daughter and son-in-law of a real-estate heiress killed on the French Riviera are among 23 people detained in the shooting death last month, prosecutors said Tuesday, laying out an investigation that drew in surveillance footage tracing suspects up the coast, suspicious money transfers and shower gel DNA.

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 the scene.

Marseille prosecutor Brice Robin said among were Pastor's daughter, Sylvia, and her husband Wojciech Janowski, Monaco's honorary Polish consul. Janowski's bank account showed suspicious movement, Robin said, but the son-in-law had no direct contact with the two men suspected of carrying out the shooting.

The two suspected assailants were also arrested in the police sweeps Monday in the cities of Rennes, Marseille and Nice. Among others detained were suspected intermediaries and people "in the know" about the plot, Robin said.

Police tracked down the two suspected attackers by tracing surveillance footage from the moment they boarded a train in Marseille, to the hospital grounds in Nice, and back to Marseille, said Robin. He said both shooting suspects had served time in French prisons for lesser crimes. DNA evidence from one of the men was found on some hotel shower gel and matched against French authorities' DNA database, Robin said.

"I would say they were only moderately professional for this kind of work," Robin said. He identified them as Samine Said Hamed, 24, and Alhaire Hamadi, 31.

The spokesman for Poland's Foreign Ministry, Marcin Wojciechowski, wrote in a tweet that Janowski would be dismissed.

Robin offered no possible motives, beyond saying that Helene Pastor, who had only two children, regularly gave money to Sylvia Pastor.