Arnoud van Doorn, who quit the far-right Freedom Party in 2012 to convert to Islam, was detained in the Hague over the alleged plot. He was released without charge on Monday but police said an investigation was ongoing.
Also on Monday police announced they had stepped up security for Rutte, who is known for cycling to work with little or no security, over fears he could be targeted for kidnapping or attack by drug gangs.
Police said they arrested van Doorn after he was seen 'acting suspiciously' in the same area of the Hague as Rutte.
The prosecutor's office said van Doorn appeared to be gathering information for 'preparation of attempted murder', without elaborating.
But his lawyer Anis Boumanjal said van Doorn had only been in the Hague for an hour prior to his arrest and was in the area to give his mother's cat medication.
In that time he stopped for coffee at a café that was coincidentally opposite the gym where Rutte was exercising and then just happened to walk past a BMW believed to be carrying the PM.
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Dutch politician is arrested over plot to KILL Prime Minister Mark Rutte | Daily Mail Online