Military police are to lead a renewed search for the daughter of a British soldier who disappeared from a barracks shop in Germany 36 years ago.

A hundred soldiers will spend five weeks on a forensic excavation of the banks of the river Alme in Paderborn, a city in eastern North Rhine-Westphalia, where Katrice Lee, two, disappeared after wandering off in a Naafi shopping centre.

The Royal Military Police (RMP) reopened the investigation in 2012, with reanalysed evidence identifying the riverbank as being of particular interest. The case featured on the BBC’s Crimewatch series last year.

Katrice was shopping with her mother when she went missing from the Naafi in Schloss Neuhaus, near the military base where her father, a sergeant major, was stationed.

It was 28 November 1981, her second birthday, and they were buying treats for a birthday tea. Sharon Lee, 64, said her daughter was gone “in a matter of seconds”.

Efit of a suspect in the disappearance of Katrice Lee. Photograph: MoD/PA

“Katrice wouldn’t sit in the trolley, so I carried her all the way around in my arms doing my shopping,” she told the Sun. “When we got to the checkout I realised I’d forgotten crisps. I put Katrice down and said to my sister Wendy: ‘Just keep an eye on her while I go back to the crisps stand’. It wasn’t far away. It took me about 40 seconds, a minute at most.”

When she returned, Katrice was gone. “My sister said: ‘I thought she was with you. She ran and followed you.’” British soldiers and military police, German police and volunteers searched widely, but the girl was never found.

Military police began investigating Katrice’s disappearance again in 2012. Warrant Officer Class 1 Richard O’Leary, the RMP’s senior investigating officer in the case, said his team had identified the bank of the Alme at Paderborner Str as important.

“In February 2017, the case featured on BBC Crimewatch,” said O’Leary. “As part of the feature a photofit was released of a man seen at the Naafi on the day Katrice disappeared, holding a child similar to Katrice and getting into a green saloon car. We are keen to hear from anyone who could help to identify this person.

Age progression photo of Katrice Lee as she may look at 38. Photograph: MoD/PA

“A green saloon car was also seen on the river Alme bridge near the Naafi the day after Katrice disappeared. It may or may not be the same car, but we are very keen to identify it.

“We are appealing to members of the public and the military community, including veterans and retired civil servants in both Germany and the UK: do you know what happened to Katrice?”

Investigators have not ruled out the possibility that Katrice remains alive. They said she was born with an unusual eye condition in her left eye and it would take two medical operations to correct it. An age progression image of what Katrice may look like now, aged 38, has been produced.

O’Leary said: “If anyone feels they know someone who looks like this, or believes they could be Katrice, then we would encourage them to come forward.”