The woman, married to a banker, was found dead near her home in Heidenheim in 2010. She had been kidnapped and fatally stabbed.
The 47-year-old suspect had denied murder and police said they had failed to match his DNA to the crime scene.
The woman's husband, who was head of a local bank, killed himself in 2011.
After the kidnapping in May 2010 he left €300,000 (£257,000) in ransom money at an agreed spot by the A7 trunk road, near Heidenheim, but it was never collected. Heidenheim lies 86km (53 miles) from the south-western city Stuttgart.
Contact with the kidnapper was lost and Maria Bögerl's body was discovered near a woodland the following month.
Police said that last July the man had told witnesses while he was drunk that he had carried out the murder. The conversation had been recorded on a mobile phone and had then been given to the police.
However, the suspect was only identified after a TV appeal on Wednesday night. He was arrested shortly afterwards at his home a few kilometres from Heidenheim.
He was released after detectives established that his DNA did not match traces found in the car used to abduct Maria Bögerl. Police said inquiries into the man would continue.
Police in southern Germany have freed a man they arrested over the 2010 kidnap and murder of Maria Bögerl - one of the country's biggest unsolved crimes.