Police arrest 73yo accused of being SA's 'bicycle bandit' after nearly ...

South Australia Police believe they have caught the so-called 'bicycle bandit', who robbed banks across small towns over a 10-year period, often making his escape on a bicycle.

Key points:Police arrest a 73-year-old man from Adelaide's south over 10 aggravated robberies and one attempted aggravated robberyPolice believe him to be the 'bicycle bandit', who robbed banks in small SA towns over a 10-year periodThe offender would often escape on a bicycle

For nearly 20 years, police have been searching for the person responsible for a spate of armed bank robberies from 2004 to 2014.

On Friday, officers arrested a 73-year-old man from O'Sullivan Beach, in Adelaide's south, for 10 aggravated robberies using a firearm and one attempted aggravated robbery using a firearm.

Investigators allegedly found ammunition and six unregistered guns at the suspect's address.

Detective Superintendent Billy Thompson from SA Police's Serious and Organised Crime Branch said the arrest was the result of a "painstaking" investigation.

"Over the course of a decade, it is alleged this person committed 10 significant bank robberies, stealing substantial amounts of cash," he said.

Police said the first robbery took place in May 2004 at an ANZ branch in Mannum, in South Australia's Murraylands.

The offender was dubbed the 'bicycle bandit' for his unusual choice of getaway vehicle.(Supplied)

From July 2004 to June 2009, robberies occurred at banks in various towns including Lobethal, Blackwood, Mount Pleasant, Tanunda, Yankalilla, Balaklava and Willunga, with a total of more than $250,000 stolen.

In 2008, BankSA offered a $25,000 reward to catch the robber, who had been dubbed the 'bicycle bandit' due to his regular choice of getaway vehicle.

Then, in September 2014, a BankSA branch at Mount Pleasant was robbed by an offender who fired several shots before escaping with cash.

At the time, police were investigating whether the 'bicycle bandit' was responsible due to what they described as "striking similarities" between the robberies. 

Detective Superintendent Billy Thompson says the matter is now before the courts. (ABC News: Ethan Rix)

On Sunday, Detective Superintendent Thompson said police realised early on that they were potentially dealing with a "serial bank robber".

"The modus operandi that [was] used on each robbery was very, very similar, strikingly similar," he said.

Detective Superintendent Thompson said there had "literally been hundreds of people looked at" over the last two decades, but said the 73-year-old man only became a person of interest "very recently".

"I think this is probably the longest ongoing Serious and Organised Crime investigation in South Australia of this nature," he said.

He said police hoped the arrest would bring "some comfort" to the victims.

"The arrest on Friday closes another chapter in this long-running investigation," he said.

"I hope it will go some way to bringing relief to all the victims who were affected by the fear and trauma of these events over the years."

"Nineteen years is a long time, but we got there."

Police said the 73-year-old man will appear in court tomorrow.