An employee at Walmart in Petal had a feeling something wasn't right when he encountered a customer Friday afternoon.

The customer, identified by police during a news conference Tuesday as 22-year-old Patsy Victorius Delvecchio III, was seen at the store carrying a handgun in his waistband, asking questions that made the employee feel uncomfortable.

Delvecchio, who had purchased some ammunition, left the store but remained in his vehicle for about 15 minutes, which also made other people who observed him feel uneasy, Police Chief Matthew Hiatt said.

After interacting with Delvecchio, the employee contacted a store manager, who then called the police.

When asked if he believed the actions taken by the Walmart employee, police and others helped saved lives, Hiatt responded, "I would absolutely say that."

"It began certainly with the employee, with Walmart," he said. "It's my understanding that there were some concerned citizens as well that was bringing the actions of Mr. Delvecchio to the attention of Walmart staff.

"That's what it takes. We have to have the assistance and willingness of the public."

Petal Mayor Hal Marx said he is grateful police and the ATF were able to curtail Delvecchio's actions before the situation escalated.

"As a civilian who has been informed of all the actions that took place, I have no doubt that lives have been saved," he said. "I think this is a perfect example of how in our country people are aware and cooperating with law enforcement … we need to make sure that we have a safe community."

An officer who had arrived at the store saw Delvecchio's vehicle leave the Walmart parking lot and conducted a traffic stop. The officer noticed the gun in Delvecchio's waistband and also saw an assault rifle style of weapon and about 500 rounds ammunition in the vehicle, Hiatt said.

Officers also saw a notebook that had a note to "buy more ammo" written on it.

"I'd hate to think, I'd hate to know (how much damage could have been caused)," Hiatt said. "Thank the Lord we don't have to find that out this time."

Delvecchio at that time was released since he had not committed a crime.

After the traffic stop officers and store managers reviewed security video and police became concerned about Delvecchio's behavior.

Around 11 a.m. Saturday, Delvecchio was seen traveling west on Evelyn Gandy Parkway, where he was stopped by police and taken into custody for questioning. Delvecchio's vehicle was towed to the police station.

Bureau of Alcohol, Tobacco, Firearms and explosives Special Agent Jason Denham was contacted and arrived at the scene to assist Petal police in the interview.

After the interview, a PPD crisis intervention team officer determined Delvecchio should be placed at a single-point-of-entry facility for evaluation. He was placed under a 72-hour hold.

A Pine Belt clinician who examined Delvecchio told police he needed further evaluation.

Hiatt said Delvecchio will remain in custody until the evaluation is complete. The next course of action will be determined once information from the evaluation is available.

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Delvecchio, who has served in the military, has not been charged with any crime, but could face charges after the investigation and psychiatric evaluation is complete.

Denham said Delvecchio could face federal charges for the weapons, but it is too early to determine what he might be charged with.

Hiatt said while he is concerned about Delvecchio's well-being, he also must think about the public's safety. The department is taking the situation seriously, and will not tolerate anyone who is thinking of causing harm.

"I hope we've set the tone and made an example Petal Police Department and Special Agent Denham and his (ATF) members that this kind of behavior will not be tolerated," Hiatt said.

"The city, the country is at an alerted state of awareness of what's going on so when these types of situations happen we're going to address the situation accordingly. We're going to respond."

A Walmart spokesperson emailed a response to the incident:

“Customer and associate safety is our top priority. We appreciate our associate for their quick attention to something that looked suspicious. We immediately contacted police and are grateful to the Petal Police Department for their quick response and apprehension of the suspect.”

Police do not believe anyone else is involved in the incident and Delvecchio was acting alone.

"There is nothing to indicate to us that Mr. Delvecchio is working in cahoots with anyone else," Hiatt said. 'This seems to be an isolated incident with him and him alone."

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Contact Lici Beveridge at 601-584-3104 or lbeveridge@gannett.com. Follow her on Twitter @licibev.