The suspect is the girl's step-uncle, 32-year-old Peter John, and police said he is considered dangerous. He allegedly placed a bomb in a letterbox at her family's home in Berlin's Rudow district that exploded as she opened it.
Later that week, police located the booby-trapped red BMW of the suspect, but he remains on the run and the authorities have sealed off his apartment.
Doctors have been frantically trying to save the girl's life and they said there's now a good chance they will be able to save her arm. But the girl, Charlyn, remains in critical condition at a Berlin hospital.
The suspect also allegedly put a bomb on the roof of the car of Charlyn's father, but he handed it over to police after it did not explode.
Police believe the bombing was part of a long-running family feud. The father reportedly revealed during police questioning last Thursday that he suspected someone in his extended family might want to harm his immediate family, but refused to comment further.