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French radio station RTL was the first to report that a woman had been identified and taken into custody in Landerneau, an area in Brittany, not too far from where the crash took place.
After the crash, which saw riders such as former world champion Tony Martin hit the floor, the organisers of the race said that they would be taking action against the person responsible once they were found, and French police quickly started an investigation to find the culprit.
The woman stands accused of involuntarily causing injury and could face a 1,500 euro fine if found guilty.
The crash - one of several that occurred on Saturday's first stage - happened with about 45 kilometres left for the riders.
The woman stepped into the road bearing a sign that read 'Allez Opi-Omi' - which is a German term for grandparents - with her back to the onrushing peloton.
Tony Martin then collided with the sign, sparking a huge wave of crashes that left riders with visible injuries.
In protest for their safety, following further crashes on the following stages, the riders decided to stop for a minute just one kilometre into the fourth stage on Monday, before riding the next 10 kilometres at a very slow pace.
Today, the rider's union (CPA) called for cycling's governing body, the International Cycling Union (UCI), to show them a bit more respect.
They said: "Following the crashes during the third stage of the Tour de France, the riders have been discussing how they wish to proceed to show their dissatisfaction with safety measures in place and demand their concerns are taken seriously,
"Their frustration about foreseeable and preventable action is enormous."
Speaking of their decision to pursue legal action against the person responsible for Saturday's crash, Tour de France deputy director Pierre-Yves Thouault said: "We are doing this so that the tiny minority of people who do this don't spoil the show for everyone."
As well as the police fine, the consequences for the crash could be worse should individual riders decide to take legal action.
At least one cyclist - Team DSM's Jasha Suetterlin - has indicated that he will pursue legal action.
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