Through his credit card receipts at hotels, restaurants, and rental car agencies, investigators began to piece together Unterweger's movements. Over several months of detective work, they placed him in Graz
in October when Brunhilde Masser was murdered and again in March when Elfriede Schrempf disappeared. He was in Bregenz in December when Heidemarie Hammerer was taken, and a witness said that Unterweger resembled the man with whom Hammerer was last seen. On that night, this witness said, the man had worn a brown leather jacket and red knit scarf.
They also determined that Unterweger had been in Prague the previous September. Contacting authorities there, they learned that his visit had coincided with the unsolved murder of another woman, Blanca Bockova. She had been found in the woods, covered in dirt and leaves, and wearing only socks. She had been strangled with an undergarment, and her jewelry had been left alone. The signature was clear. There were several very precise details that matched up across the crimes.
When the four women had been abducted and murdered in Vienna, Unterweger was there as well. While none of this was proof that would stand up in court, there was enough evidence to warrant an interview with Unterweger. They pondered how this move might affect him.