An office secretary opened the wooden box after a messenger delivered it to a law office on Thursday, and two homemade explosives inside went off, killing her and seriously injuring a lawyer.
Judicial police apprehended the suspect at his mother's home, where he was living, the two police officials said on condition of anonymity because the investigation was ongoing.
The suspect, said to be a 45-year-old architect, had allegedly harassed a lawyer at the firm two years ago, the officials said.
Prosecutor Jean-Claude Marin has said the package appeared to have been addressed to the law firm, which handles civil and commercial cases.
The office was located in a building that also housed another law firm co-founded by French President Nicolas Sarkozy and a Holocaust research foundation, though officials said they did not appear to be targeted.
After the arrest Friday, authorities continued to search for a delivery woman who dropped off the package, the officials said.
An official close to the investigation said the bombing did not bear the hallmarks of Islamic or Corsican terrorists, who have staged attacks in France in the past but often use bigger bombs and different methods. The official spoke on condition of anonymity because of the sensitivity of the case.
Police investigators were questioning the suspect on Friday.
Güncelleme Tarihi: 07 Aralık 2007, 18:19