Rotterdam - Dutch police on Thursday released a van driver arrested over a suspected terror attack plot on a Rotterdam concert venue, but stepped up inquiries based on a "concrete" tip-off from Spain."The man was freed earlier this evening and is no longer a suspect in the investigation," Rotterdam police said in a statement.It remained unclear whether the tip-off by Spanish officials to the Dutch was linked to last week's deadly attacks in Catalonia. Nor was it clear when the Spanish learned of the threat.The twin vehicle attacks in northwest Spain killed 15 people and wounded 120 others.Dutch investigators are still trying to piece together the events that led to the cancellation of Wednesday night's concert by Californian rock band Allah-Las.READ: Muslims rally in Spain against terrorism after attacksThreatening statementsEarlier on Thursday, Rotterdam police chief Frank Paauw said: "There was concrete information from the Spanish police that an attack would be committed on that date, at this place and against this rock band."After cancelling the planned concert by the Allah-Las, police carried out a pre-dawn raid where they arrested "a 22-year-old man regarding the terror threat Wednesday evening in Rotterdam", a police statement said.BNR radio cited sources that the man had been arrested after "making threatening statements" over the messaging app Telegram, said to be popular with terror groups.Justice Minister Stef Blok later told BNR radio the authorities were "keen to hear why he had done something so idiotic".This man was still in detention, said Paauw, "suspected of being involved in preparations for a terror attack".Dutch national news agency ANP said the suspect was most likely a student from the small town of Zevenbergen, described by neighbours as "a quiet youngster with a girlfriend".The driver of the Spanish-plated van was arrested Wednesday evening, August 23, after police noticed him driving in a suspicious way, near the concert venue at the Maassilo, in the city's sprawling harbour district.Even on Wednesday, however, there were doubts that he was in fact linked to the threat.While officers found a "couple of gas canisters" in the van, the driver was a mechanic who "appeared to be under the influence of an alcoholic substance", police said.Spanish police also ruled the man out of the inquiry. They said he had "five gas canisters in his van for domestic use" but was completely drunk.Police chief Paauw said it looked as if "the man had had the bad luck to be in the wrong place at the wrong time".The threat on the concert venue recalls previous such attacks.In May, 22 people were killed in a suicide bombing at a concert by US singer Ariana Grande in the northern English city of Manchester.And in November 2015, 90 people were killed in Paris at the Bataclan concert hall where US rock band Eagles of Death Metal was playing.That was part of a co-ordinated jihadist attack on the city that night which claimed 130 lives.