US  investigators have questioned the wife of the gunman who killed 49 people at a gay nightclub in Orlando, the FBI said on Wednesday, and a law enforcement source said she could face criminal charges if there is evidence of any wrongdoing.

Omar Mateen's wife, Noor Salman, knew of his plans for what became the deadliest mass shooting in modern US history, said the law enforcement source, who has been briefed on the matter.

"With respect to the wife, I can tell you that is only one of many interviews that we have done and will continue to do in this investigation," FBI Special Agent Ron Hopper told a news conference. "I cannot comment on the outcome or the outcome of that investigation."

CNN, citing law enforcement officials, said a US. attorney planned to present evidence to a federal grand jury to determine whether charges would be brought against Salman. She could not be reached for comment.

The first memorial for a victim of the Pulse nightclub massacre, a wake for Javier Jorge Reyes, was held on Wednesday evening at a funeral home near a four-lane highway just south of Orlando. Motorists honked their support for the attendees, many of whom held signs or wore T-shirts reading: "Orlando Strong."

In Washington, Sunday's shooting in Florida stirred fresh debate on gun purchases in the United States because Mateen was legally able to buy an assault rifle even though the FBI had investigated him in the past for possible ties to Islamist militant groups.

Republican presidential candidate Donald Trump said he would meet the powerful National Rifle Association lobbying group, which has endorsed him, to discuss limited gun control measures. That marked a break with Republican Party orthodoxy, which typically opposes any restrictions on gun ownership.

The NRA responded that it believed that people listed on terrorism watch lists should face additional reviews before purchasing firearms.

SELF-RADICALIZED

Mateen's wife was with him when he cased possible targets in the past two months, including the Walt Disney World Resort in April, a shopping complex called Disney Springs and the Pulse nightclub in early June, CNN and NBC reported.

The gunman's first wife, Sitora Yusifiy, says Mateen beat her and forced her to split from him after only four months of marriage.

Mateen, a New York-born U.S. citizen of Afghan heritage, was shot dead by police after a three-hour rampage through the nightclub.

Federal investigators have said Mateen, 29, who worked as a security guard, was likely self-radicalized and there was no evidence he received any help or instructions from outside groups such as Islamic State.

However, even as his victims lay dead around him, Mateen posted messages on Facebook pledging allegiance to Islamic State's reclusive leader Abu Bakr al-Baghdadi, Fox News said.

"The real muslims will never accept the filthy ways of the west...You kill innocent women and children by doing us airstrikes...now taste the Islamic state vengeance," he wrote from the club, according to Fox News. The broadcaster cited Senator Ron Johnson, chairman of the Senate Homeland Security Committee.

Mateen's social media accounts were taken down before they could be viewed widely by the public but committee investigators uncovered some or all of them, Fox News said.

Mateen also made calls to 911 emergency services during his rampage, which he used to declare his allegiance to various Islamist militant groups, some of which are at odds with one another.

A video clip emerged on Wednesday showing Mateen cursing and flippantly discussing the 2010 oil spill in the Gulf of Mexico. He was filmed secretly for a documentary about the spill, "The Big Fix," while he worked as a security guard where some of the spill cleanup was taking place in Florida.

The Federal Bureau of Investigation questioned Mateen in 2013 and 2014 for suspected ties to Islamist militants but concluded he did not pose a threat.

SCENE INSIDE CLUB

Orange County Medical Examiner Joshua Stephany came across a chilling scene inside the club after the shooting ended.

"It's almost like time stopped. There were still background TVs playing, lights blinking, drinks that had just been poured, checks that were about to be paid, food half-eaten. That's not even thinking about the bodies on the ground," he told CNN.

US. Senator Pat Toomey, a Republican who joined Democrats in an unsuccessful push for gun control legislation after the killing of elementary school children in Connecticut in 2012, is working on a bill to keep guns out of the hands of people on terrorism watch lists, a gun control group said on Wednesday.

President Barack Obama and Vice President Joe Biden will visit Orlando on Thursday to meet the families of victims in the attack, the deadliest on US. soil since the hijacked plane attacks on New York and Washington on Sept. 11, 2001.

"The president, while he's there, will also have an opportunity to speak publicly about what he sees and also about the message that he's preparing to deliver on behalf of the country to make clear that the country stands with the people of Orlando, stands with the LGBT community in Orlando as they grieve for their loss," White House spokesman Josh Earnest told reporters.

Trump has drawn criticism from Obama as well as some senior Republicans for his proposal to temporarily ban Muslims from entering the country. On Wednesday, he also called for surveillance of mosques as part of US  counterterrorism efforts.