Prosecutors in the German city of Stuttgart are considering criminal action against students for submitting illegally issued documents, almost a year after the potential scandal came to light.

The doctor who made out the sick notes, apparently known on campus as "Doc Holiday," also remains under investigation.

University of Hohenheim officials were perplexed when dozens of students left their exam part-way through — and subsequently submitted sick notes showing ailments that were astonishingly alike.

At least 48 students abandoned their papers, mostly diagnosed with "headaches in combination with blurred vision or nausea and vomiting."

When the issue came to light in June last year, neither the students nor the doctor were expected to face prosecution.

However, prosecutors on Wednesday told the German dpa news agency they were investigating — among other leads — whether the medic had received payment. Authorities were also said to be looking at whether diagnoses were falsified systematically.

Flurry of notes in few days

The physician was found to have issued some 150 doctors' notes in total over three days, including that of the exam in question. The university's exams committee said it was dubious about 125 of the 148 sickness letters.

Read more: German high school students decry 'difficult' math tests

Some 100 students remain suspected of having taken advantage — some on more than one occasion.

Prosecution spokesman Heiner Römhild told the local Stuttgarter Zeitung and Stuttgarter Nachrichten  newspapers — which first reported the latest development — that students could face a fine or even a prison sentence of up to a year.

Under university rules, students can only skip an exam part-way through without consequence if they can show they succumbed to illness or overwhelming anxiety in a sudden and unforeseen way.

For three of the students who were caught out, the consequences were grave. They were removed from the university register — having officially failed their exam for a third and final time.