Taylor Swift Terror Plot Suspect Started Working at Venue Days Before Shows

8:30 AM -- Austrian authorities have released a few more details ... explaining the 15-year-old who was detained claims the 19-year-old asked him to secure an ignition device. Unclear if he did.

We also have further clarification on some of the chemicals found in the 19-year-old's home ... with cops saying they found a barrel of hydrogen peroxide -- used in makeshift explosives. He allegedly downloaded bomb-making instructions ... further evidence this was an amateur attempt.

Authorities say the whole of Europe's on high alert ... with concern ISIS is using Austria as an "operational area."

7:59 AM PT -- More details are emerging about the suspects' alleged actions in the lead up to their arrests ... with CNN reporting the 19-year-old suspect quit his job back in July and changed his appearance -- telling people around him he had something big planned.

Cops allegedly found 21,000 euros of counterfeit cash and a blue police light for his car to get better access to the arena's periphery. CNN says he planned to kill himself during the attack either during a standoff with police or an explosion.

CNN says the 17-year-old suspect broke up with his girlfriend recently -- possibly a trigger that sent him down this path.

Interestingly, CNN reports the 15-year-old who was detained may have just known about the plot ... and may not have played an active part in its planning.

Taylor Swift's foiled terror attack got a lot further down the road than many initially thought ... with one suspect employed by the venue just days before the singer came to town.

A 17-year-old suspect behind the near disaster in Vienna got a job at Ernst Happel Stadium in the days leading up to her shows ... seemingly to better position himself and his accomplice for their alleged terror attack. He was arrested outside the venue.

As we reported, authorities executed a search warrant at the home of one of the suspects and found chemical substances and technical devices, presumably to make a bomb. Although authorities didn't say, it appears that device could have been detonated by the 17-year-old who would have been working inside the venue.

It gets even more terrifying ... authorities now say this would have been a multi-pronged attack. One of the terrorists allegedly planned to drive a vehicle into the crowd outside the venue -- Taylor typically has fans outside listening who can't get in -- and immediately thereafter a bomb would have been detonated.

Cops have also arrested a 19-year-old and detained a 15-year-old ... claiming the three individuals planned the attack.

A photo of the purported 19-year-old suspect has been circulating in foreign media, showing him with machetes -- and he reportedly planned to use knives and machetes during the attack.

General Director for Public Security Franz Ruf says the suspects showed "concrete preparatory actions" in the lead-up ... and, it's no surprise authorities are calling this a "serious terror plot."

As we told you ... authorities say they feel confident they've minimized the threat of the same attack -- but, the shows were canceled anyway because of the "abstract" threat of attack.

Austrian officials claim their main suspect -- the 19-year-old -- has fully confessed to the attack plans ... with Director of State Security and Intelligence Omar Haijawi-Pirchner claiming the suspect felt it morally "right to kill infidels." Authorities say all 3 suspects were radicalized online in the last month.

Nearly 200k people were expected between the three shows, but Barracuda Music said they felt they needed to pull the plug immediately -- offering full refunds to the legion of disappointed fans.

The Vienna Tourist Board posted a condolence to all the Swifties ... little comfort to the thousands of fans who flooded into the city to see the global pop sensation.