Fabrice Anthamatten, 39, was arrested in the Polish-German border area on Sunday on an international warrant days after he and his therapist went missing in Switzerland during a prison-approved outing.
"The prosecutor's office is currently questioning the man," Malgorzata Wojciechowicz, spokeswoman for the regional office in the northwestern city of Szczecin, told AFP.
"We're waiting for files from Switzerland to complete the extradition proceedings."
German officers arrested Anthamatten in the Polish border village of Kolbaskowo after a cross-border pursuit. They then handed him over to Polish police.
Anthamatten — a dual Swiss and French national with a criminal record in both countries — was arrested behind the wheel of the car in which he was believed to have fled Switzerland on Thursday.
He is the prime suspect in the murder of prison therapist Adeline Morel.
Her body was found near Geneva on Friday, a day after they left the prison for a trip to a horse-riding centre that was part of Anthamatten's prison therapy.
Interpol issued a warrant for him at Switzerland's behest, and police on Friday locked onto the victim's mobile signal near the northern Swiss border city of Basel.
Sniffer dogs then picked up his trail at a train station just inside Germany.
Morel, 34 and the mother of an eight-month-old child, had accompanied Anthamatten alone on what was only his second day-release from a Geneva detention facility.
Anthamatten was serving 15 years for a rape committed in France while he was on parole in Switzerland, where he had already been sentenced in another rape case.
French justice officials had allowed him to be transferred to a Swiss jail to serve his sentence.