As the attack happened, Malik posted a pledge of allegiance to ISIS leader Abu Bakr al-Baghdadi on Facebook, three U.S. officials familiar with the investigation told CNN.
Here are other individuals in the United States who allegedly became inspired by ISIS.
In May, Elton Simpson and Nadir Soofi opened fire
outside a Prophet Mohammed cartoon contest in the Dallas suburb of Garland, Texas, wounding a security guard before police shot and killed them.
ISIS claimed responsibility two days after the attack,
but there was no indication that the terror group in Iraq and Syria had contact with Simpson or Soofi, who both lived in Phoenix.
Moments before the attack, Simpson posted a tweet with the hashtag #texasattack: "May Allah accept us as mujahideen."
The tweet said he and his fellow attacker had pledged allegiance to "Amirul Mu'mineen," which means "the leader of the faithful." That likely refers to al-Baghdadi, CNN terrorism analyst Paul Cruickshank said.
Earlier, Simpson had asked his followers on Twitter to follow an ISIS propagandist.
After the shooting, the propagandist tweeted: "Allahu Akbar!!!! 2 of our brothers just opened fire."
Both Twitter accounts were deactivated.
The gunmen may have plotted the attack without formal direction from ISIS, former FBI agent Tim Clemente said.
Wanting to become an ISIS bride
In 2014, Shannon Maureen Conley of Colorado, then 19, wanted to become an ISIS bride and join its jihad in the Mideast.
She was at Denver International Airport, where she was going to fly Turkey and await word there from an ISIS member in Syria, a man she met on the Internet and planned to marry, authorities said.
A certified nurse's aide in Colorado, Conley intended to become a nurse in an ISIS camp, authorities alleged.
Her parents, Ana Maria and John Conley, were aware of their daughter's conversion to Islam but didn't know about her interest in extreme Islam or jihad.
She adopted the Muslim name of Halima after converting to Islam, but while in jail, she changed it to Amatullah, which means female "servant of Allah."
A federal judge sentenced her to four years in prison
after she admitted guilt to a conspiracy charge to support ISIS.
"Even though I was committed to the idea of jihad, I didn't want to hurt anyone. It was all about defending Muslims," she said at her sentencing.
Inviting mom and dad to join ISIS
In Illinois last year, Mohammed Hamzah Khan, 19, allegedly had invited his family to join him in his plans to travel to join ISIS in the Mideast and was eventually charged with trying to support ISIS.
Outside a courtroom earlier this year where her son pleaded not guilty, Zarine Khan condemned ISIS and accused it of using social media propaganda to brainwash Muslim youths.
"We condemn this violence in the strongest possible terms. We condemn the brutal tactics of ISIS and groups like them. And we condemn the brainwashing and the recruiting of children through the use of social media and Internet," the mother told reporters while reading tearfully from a statement.
"We have a message for ISIS, Mr. Baghdadi and his fellow social media recruiters: Leave our children alone!" Zarine Khan said, as her husband, Shafi Ullah Khan, stood beside her.
She was referring to Abu Bakr al-Baghdadi.
The teenager allegedly wrote that he was leaving the United States to join ISIS, and authorities found a three-page letter in the bedroom he shared with a sibling in Bolingbrook, Illinois, in which he invited his family to join him. But he warned them not to tell anyone about his travel plans, the complaint said.
A round-trip ticket was purchased for Khan from Chicago to Istanbul, and he was arrested at O'Hare International Airport in Chicago in 2014.
In October, Khan, now 20, pleaded guilty to one count of attempting to provide material support to ISIS, prosecutors said.
'Peer-to-peer recruiting' among young men
Earlier this year, a group of six young Minnesota men were arrested and accused of conspiring to sneak into Syria and join ISIS
"by any means necessary," federal prosecutors said.
They were all friends, ages 19 to 21. Recruiting for the ISIS terrorist network is a particular problem in Minnesota's community of Somali immigrants.
"What's remarkable about this case was that nothing stopped these defendants from plotting their goal," said U.S. Attorney Andrew M. Luger.
"People often ask who is doing the recruiting and when will we catch the person responsible," Luger said. "But it is not that simple. In today's case, the answer is that this group of friends is recruiting each other. They're engaged in what we describe as peer-to-peer recruiting."
Zacharia Yusuf Abdurahman, 19, Adnan Farah, 19, Hanad Mustafe Musse, 19, and Guled Ali Omar, 20, were arrested last April in Minneapolis. Abdirahman Yasin Daud, 21, and Mohamed Abdihamid Farah, 21, were arrested in San Diego after driving there in hopes of crossing into Mexico.
The men spent 10 months plotting, authorities said.
Another friend, who was part of the group, allegedly changed his mind and became a cooperating witness for the FBI, tape-recording some meetings.
Abdurahman and Musse have pleaded guilty to conspiring to try to help ISIS, prosecutors said.
The cases against the other defendants are still pending, according to court records.
Tweeting in support of ISIS
In August 2014, Donald Ray Morgan was arrested on arrival at New York's John F. Kennedy International Airport from Frankfurt, Germany, and was accused of being a sympathizer of ISIS.
The court documents make no mention of the ISIS connection, but U.S. officials say what drew their attention is Morgan's online activities, making Twitter postings in support of ISIS.
Morgan was considered to be more of an "aspirational" supporter of ISIS.
A New York Daily News report cited officials alleging that Morgan used the moniker Abu Omar al Amreeki to publish tweets in support of ISIS while he spent time in Lebanon. At the time of Morgan's arrest, a public defender assigned to represent Morgan said there was no evidence Morgan tried to support ISIS, the newspaper said.
In October 2014, Morgan pleaded guilty to attempting to provide material support to ISIS, prosecutors said.
At least once, Morgan unsuccessfully tried to travel from Lebanon to Syria to join ISIS, and he also often used social media and an interview with an American journalist to express his support for ISIS and violent terrorist activities, prosecutors said.