DALLAS - After a massive police presence, school and businesses locked down, and a SWAT deployment, Dallas police said reports that an active shooter was firing a weapon from an apartment complex Tuesday morning might not have been correct.

Police took David Arnold Lamb, 38, into custody on Tuesday afternoon after an intense three-hour standoff.

'Well, I don't believe he had a gun. He's just not that type,' said Margarete Lamb, David's mother.

She also told News 8 that she thinks her son's mental condition might have led to the incident.

'He was on medication. I just figure he got off his medication,' Mrs. Lamb said. He suffered from 'bipolar [disorder] and several other different things,' she added.

Police sources said Lamb was taken to Parkland Hospital for a mental evaluation.

The standoff ended after SWAT shot tear gas canisters into Lamb's fifth floor apartment at The Vista in the 2300 block of North Houston Street.

Police said he was apprehended as he opened his door after the tear gas was used.

Investigators said police were originally called to the complex after staff members there reported hearing gunshots.

However, police never found a firearm after an exhaustive search of the apartment. Late Tuesday, police suggested the original witnesses might have heard something else they mistook for gunshots.

Lamb's only criminal record is a DWI. Last month, an arrest warrant was issued for Lamb after his probation on a 2012 DWI conviction was revoked.

He moved to Dallas four years ago, his mother said, and ran a residential cleaning service. Lamb lived in the apartment by himself.

A neighbor who didn't want to be identified said Lamb would frequently answer the door in the nude and often left his door open. The neighbor said that people were constantly coming in and out of the apartment.

Authorities were called Vista Apartments about 10 a.m. Tuesday after shots were 'shots being fired from an apartment and windows being shot out,' said Dep. Chief Scott Walton.

Patrol officers 'got to the scene and realized that there could be an armed individual there who was shooting from an elevated position, really realized this was a very dangerous situation and called for SWAT officers to respond,' Walton said.

Residents at the Vista Apartments complex were warned to stay inside their residences through an e-mail.

'We are dealing with an emergency situation at this time,' read an e-mail from Vista Management. 'There is an armed individual on site and the police are actively attempting to control the situation. Please REMAIN INSIDE YOUR APARTMENTS until further notice.'

The occupants of the apartment where the standoff had recently had an eviction case filed against them. However, police later said the eviction case wasn't related to the standoff.

'We knew he was under distress, but I don't want to speculate on what caused him to take the actions that he did,' Walton said.

A resident on the second floor of the building described her fear when she first heard loud voices outside her apartment.

'I heard some screaming outside in our hallway,' said Laci, who didn't want her last name disclosed. '[...]So, I've been hiding in my closet. They just told me it's on the fifth floor, so that makes me feel a little bit better.'

Laci said she received the e-mail warning residents at about 10:30 a.m.

A loud bang boomed across the area after noon and a plume smoke billowed from the building. Through Twitter, police confirmed 'SWAT just set off a flash bang as a distraction device.'

'A flash-bang is a distraction device that produces a loud noise and brilliant flash of light designed to distract and disorient a suspect,' said Lt. Max Geron.

Three more bangs and more smoke came from apartments at about 12:46 p.m. as Dallas police announced they deployed more flashbangs at the site of the standoff.

Minutes later, police announced the suspect was taken into custody.

As police swarmed the area, they warned nearby businesses to lockdown or close.

The nearby AT&T Performing Arts Center, Perot Museum, W Hotel, Dallas Aquarium, Lunar Prep Academy, and Booker T. Washington High School were among places that closed their doors and kept visitors, students and staff inside. The House of Blues also closed.

That meant restaurants had to turn away customers, apartments and hotels locked its doors, and children at the downtown attractions were forced to stay inside.

'They kept it really quiet in [the Perot Museum,]' Priya Vengurlekar said. 'The kids didn't know anything, so it was great.'

If you were inside, you stayed inside. Close to 1,500 schoolchildren on field trips at the Perot Museum stayed a little longer.

Right across the street from the Vista Apartments, workers at the construction site had to evacuate, too.

Workers were told to put down tools and move away from the glass, out of fear of the gunman shooting out of his apartment.

The kitchens of nearby restaurants on Houston street were also shut down during what is a normally very busy lunch hour.

After the all clear, people from the hotels and apartments nearby finally trickled out.

WFAA's Marie Saavedra and Jobin Panicker contributed to this report.

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