The wife of the gunman who carried out the terror attack in Orlando, Florida, bought ammunition with her husband, CBS News homeland security correspondent Jeff Pegues reports.

Law enforcement sources told CBS News that video footage from a store shows Noor Salman buying ammunition with Omar Mateen.

On Sunday, Mateen carried out the deadliest terror attack on U.S. soil since 9/11 by going on a shooting rampage at the Pulse nightclub, which left 49 people dead and more than 50 others injured, some critically.

Investigators believe Salman drove with Mateen to case the club prior to the attack, Pegues reports.

On Tuesday, a law enforcement source told CBS News that Salman told FBI investigators she tried to stop her husband from committing the attack.

It's not clear whether she knew the extent of what Mateen had planned.

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On Wednesday, the FBI urged people who have had any contact or know anything about Mateen to contact them. FBI agent Ron Hopper said no piece of information was too small.

The FBI is characterizing the shooting at Pulse, a gay nightclub, as both a terrorist attack and a hate crime, CBS News' Paula Reid reported.

A source familiar with the investigation tells CBS News gunman Mateen referenced the Islamic State of Iraq and Syria (ISIS) in a Facebook message posted moments before the shooting.

"You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance [sic]," Mateen wrote, according to the source.

"In the next few days you will see attacks from the Islamic State [ISIS] in the usa," the post said.

Little by little, details have begun to emerge about the 30-year-old Salman, who grew up in the small suburb of Rodeo, California, tucked in the dry hills near the oil refineries 25 miles northeast of San Francisco.

Her romance with Mateen - security guard, bodybuilder and devout Muslim - began online, according to a neighbor, and they were married on Sept. 29, 2011, near her hometown, according to public records. The couple has a 3-year-old son.

Three people identifying themselves as FBI agents visited Salman's childhood home in Rodeo on Tuesday and spoke with her mother, said Jessie Rojas, a next-door neighbor.

In Fort Pierce, Florida, where Salman and Mateen lived, Salman made a brief visit to their first-floor apartment late Monday, escorted by police and her brother-in-law. Her father-in-law said she came to retrieve clothing. She did not speak with reporters. She has otherwise been in seclusion.

According to marriage documents on file in the Contra Costa County Recorder's office, Salman was born in the United States while her parents' birthplaces were listed as "Palestine."

It's unclear when her parents, who served as witnesses for the wedding, came to the United States, but their naturalization papers allowing them to stay in the country were approved in 1984.

No one answered the door at the Salman home Tuesday, but neighbors who know the 2004 graduate of John Swett High School in nearby Crockett said they find it hard to believe she had anything to do with the massacre.

Jasbinder Chahal, who has lived across the street from Salman's childhood home for the last 15 years, said Salman is "very nice...not the smartest, but she was beautiful.

"You know, some kids after high school, they open up the box and the world is theirs. She was inside the box, just pack it up and get married," said Chahal.

"They had a small wedding and took lots of pictures here at the house," said Chahal. The marriage license says the ceremony took place in Hercules, California, and that an imam officiated.

Of Mateen, Chahal said, "He was shorter than her and did not seem very friendly."

Chahal said Salman's mother, Ekbal Salman, was deeply upset when she visited her Monday night and said she feared for the safety of her daughter and grandson.

Salman's parents tried to shelter their four girls as they grew up.

"Noor never played in the street, and the girls were never allowed to drive," Chahal said.

The neighbor quoted Salman's mother as saying Mateen also kept her daughter from driving, until he recently allowed her to take a test to get her driver's license.

Salman's marriage to Mateen was her second, said Chahal. Mateen had previously been married as well.

Her first marriage had been arranged in the Palestinian territories by her parents, said Chahal, adding that the union did not work out.

"He was in Chicago and they were living there, but they were not married long," Chahal said. "They had cultural differences since she grew up here and was American."

Mateen had met his first wife, Sitora Yusufiy, online, too. They married in 2009 after a whirlwind romance.

Yusufiy, who immigrated to the United States from Uzbekistan, has told reporters that Mateen was mentally unstable and abusive during their brief relationship.

She said she knew quickly that the marriage had been a mistake and she left him a few months later. The couple didn't divorce, though, until June 21, 2011 - just three months before Mateen married Salman.

On one of her sister's Facebook pages - next to a family photo - there is a box with the words: "Solidarity with Gaza."

Salman rarely came home to visit after she married because Mateen would not let her, Chahal said. She quoted Salman's mother telling her that Mateen even tried to keep the daughter from traveling home to see her father when he was sick.

The younger Salman managed to scrape together the money to visit before her father died in a local hospital, Chahal said.