BERLIN — British investigators are excavating a riverbank in western Germany more than three decades after a soldier's 2-year-old daughter vanished, in a renewed push to try and find out what happened to her.

Royal Military Police are taking the lead on the investigation and are being assisted by German authorities with police dogs in their forensic search of the banks of the Alme river, in the western city of Paderborn, senior investigating officer Warrant Officer Class 1 Richard O'Leary told reporters on Thursday.

Katrice Lee vanished on her second birthday on Nov. 28, 1981, while out shopping with her mother on the outskirts of Paderborn, near the British military base where her father was stationed.

They were buying treats for the birthday party from a British military supermarket when her mother, Sharon Lee, realized in the checkout line she'd forgotten potato chips.

The mother asked her sister to watch Katrice and when she returned in what she has estimated was less than a minute, the little girl was gone. Lee's sister told her Katrice had run after her, and she thought they were together.

O'Leary said after a new review of the evidence, he was focusing on three main things: identifying a man, through a police composite, seen near the supermarket at the time of the crime with a child who looked like Katrice getting into a green car; the possibility Katrice was abducted and grew up not knowing who she was and identifying her through an age progression photo; and the investigation of the Alme river area where a green car was seen on a bridge the day after the crime.

"We're pursuing all reasonable lines of inquiry," he said.

Digging on the banks of the Alme began April 30 and is expected to go on for some five weeks, O'Leary said as soldiers worked on the scene in the background. He said they were looking for any "evidence of Katrice's disappearance, whether that's clothing or, unfortunately, Katrice herself."

O'Leary said he'd deemed the riverbank area to be "significant and of interest," but declined to give further details. "As you can appreciate this is an ongoing investigation and I don't want to release details now that might become critical later."

He said they were also trying to trace the owners of about 500 green cars who lived in the area at the time.

"That's really, really difficult as you can appreciate it was 36 years ago," he said, imploring anyone who might have any information to come forward.

Following the disappearance, broad searches of the area were conducted by British forces, German police and volunteers but no traces were ever found.

It was featured on Britain's "Crimewatch" program and Germany's "Aktenzeichen XY" in 2017 and 2018 in an effort to ensure a wide audience saw the composite of the man with the green car and the age progression photo of Katrice.

O'Leary said at the moment, however, the investigation has no suspects.

Authorities have been criticized for the initial investigation into the case and the girl's father, Richard Lee, told reporters he was still bitter, but glad O'Leary's team was looking into the evidence again.

"They are doing this to try and close the gap, to try and re-instill the trust that my family has lost," he said. "Do I forgive them? The answer is categorically no. I do not and I never will."