Police say startled shoppers at the Colorado Walmart where a shooter opened fire and killed three stalled the search process after they drew their own handguns in defense.

The shoppers' immediate response to the violent event 'absolutely slowed' investigation as it left authorities scanning through surveillance tapes in pursuit of the single armed attacker.

The few innocent yet armed individuals were eventually weeded out as suspects, amid the several hour-long investigation which began Wednesday night and into Thursday morning.

A police spokesperson confirmed after the building had been deemed 'safe enough' to enter, officials quickly began examining footage from inside the supermarket, according to The Denver Post.

'That's when we started noticing that a number of individuals had pulled weapons,' said Victor Avila, who works in part for the Thornton Police Department.

'At that point, as soon as you see that, that's the one you try to trace through the store, only to maybe find out that's not him, and we're back to ground zero again, starting to look again. That's what led to the extended time.'

The suspect, Scott Ostrem, 47, was arrested on Thursday at 8am, ten hours after allegedly opening fire at the Walmart superstore in Thornton, Colorado.

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Father-of-two Victor Vasquez was named and pictured by relatives as they raised money on social media to help his family. He was pronounced dead at the Walmart on Wednesday night

Grandfather Carlos Moreno, 66, (left) and Pam Marques, 52, also died in the shooting

Further investigation found Ostrem to be a failed businessman with astronomical credit card debt as well as a bad reputation with his neighbors.

He was arrested near an apartment complex in Twin Lakes around seven miles south of the shooting by police who received a tip that the gunman lived there.

The tipster recognized Ostrem from surveillance footage which showed him entering the store and which police released late on Wednesday as they tried to find him.

On Thursday morning, officers were already at the apartment block when Ostrem drove past in his red, four-door Mitsubishi Mirage. They chased him for a mile and then arrested him by the side of the road.

Neighbors have since described him as 'evil' and told how he walked around with a rifle bag slung over one shoulder.

As details of his Ostrem's life emerged on Thursday, including his $58,000 credit card debt and failed business attempts, the three people who died in the shooting were identified.

They are father-of-two Victor Vasquez, 26, grandfather Carlos Moreno, 66, and Pamela Vasquez, 52.

Friends of Vasquez, one of the victims, said the man had two young daughters and was expecting another child with his fiancée.

He was killed at the store in Thornton, near Denver, as he shopped with his mother and sisters in preparation for an upcoming trip. They are raising money for his funeral on a GoFundMe page.

Suspect: Scott Ostrem, 47, was arrested on Thursday. He is pictured in his mugshot that was released on Thursday afternoon

Marques' niece set up another page to raise money for her funeral expenses and family.

The woman has at least one daughter who her niece said was her 'best friend'.

It was also revealed that Ostrem was working as a sheet metal fabricator for a local roofing company and that he walked off the job at 9am on Wednesday morning without giving bosses any explanation.

Colleagues said he did not seem angry when he suddenly stopped working.

Neighbors who lived near his Denver apartment have since told how he stared out the windows of his home in Arvada and cursed at him when they said hello.

They described him as 'creepy' and 'paranoid'. A typical one-bedroom apartment in the building costs $800-a-month.

In the past few years, Ostrem has bounced between jobs after a string of failed business ventures.

They include Ostrem Installation LLC which he founded in 2012 but was which was defunct the following November.

Ostrem was arrested at 8am on Thursday after a ten-hour manhunt (left) He was seen entering the Walmart in Thornton where the shooting occurred shortly before the first reports of the shooting at 6.10pm on Wednesday (right)

He was arrested after his Mitsubishi Mirage (above) was spotted seven miles from the scene

Police arrested Ostrem at this apartment complex in Twin Lakes, around seven miles from the Walmart store, on Thursday morning when he drove past in his car. They were already there after receiving a tip that the gunman lived there

In June 2014, he founded MKA Electronics LLC but in late 2015, he filed a Chapter 7 bankruptcy claim, saying he had just $140 to his name.

He listed his assets as having a total value of $50,000 and his liabilities at between $50,000 and $100,000.

The Denver Post spoke to neighbors who said he cursed at them when they said good morning, shouting: 'Eff you' whenever he was greeted.

One said he made them 'nervous' and often carried a rifle bag.

'He made me nervous because he always had rifle in a case over his shoulder. I would know it was him. He was evil! Evil!' Teresa Muniz, one neighbor, said.

Others described him as 'creepy' and 'paranoid' and said he often was seen staring out of his window.

Ostrem's criminal past is non-violent. The first was in 1999 when he was arrested for resisting arrest.

In 2013, he was arrested in the middle of the night for drunk driving after police saw him driving erratically.

Ostrem was arrested in 2013 (left) for driving under the influence. At the time he said he was unemployed. In 2014, (right) he was arrested again in a motel after failing to appear for a court appearance for his 2013 DUI charge

A police report obtained by DailyMail.com describes how he swayed 'from side to side' as he performed field sobriety tests. At the time, he said he was unemployed.

The following year, he was arrested at a motel room for failing to appear in court to face the 2013 DUI charges. It is not known what that arrest was for or what it resulted in.

On Wednesday morning, hours before the Walmart shooting, Ostrem walked off a job without giving bosses an explanation.

'We're bewildered,' boss David Heidt told Fox News Denver.

Ostrem was arrested at 8am on Thursday morning, ten hours after allegedly opening fire.

The gunman did not say anything as he sprayed his bullets across the store. He then walked back out and fled the scene in a red, four-door Mitsubishi Mirage.

On Thursday, shoppers who abandoned their purchases on Wednesday night returned to the store. One woman was Marlena Fobb (pictured in orange pants) who hugged staff as she went back to buy a vacuum

Police do not believe the shooting is related to terrorism, but they have not ruled anything out.

On Thursday, shoppers who fled in fear of their lives as the shooting took place returned to the store to collect the personal items they had left behind.

They included a family of four who were there to buy a vacuum on Wednesday night when the shots rang out.

Marlena Fobb and her husband dropped to the ground when the shots began.

They then crawled on the ground to an office nearby that was open and waited until police cleared the store.

Marlena grabbed another person nearby and dragged them with her. A family with toddlers saw them entering the office and followed them.

Many were pictured along with Walmart staff standing outside the store as emergency workers closed off the scene.

The shooting happened around 6pm local time inside the crowded retail store. Above employees and shoppers leave the scene