In the wake of the mass shooting in Orlando, law enforcement officials in New Jersey have released a list of terrorist groups they are watching as they work to detect threats made by both domestic and international groups.

Mateen, an American citizen, had previously been on an FBI watch list, but because of a lack of evidence that he posed a legitimate threat, the investigation was closed.

New Jersey's Homeland Security Office shared the list after the attack at the gay nightclub in Florida left at least 49 people dead. It was the worst mass shooting in U.S. history. The shooter, 29-year-old Omar Mateen , called 911 and pledged allegiance to ISIS during the attacks, officials have said.

The case illustrates the challenge law enforcement across the county, including in New Jersey, face with detecting homegrown terrorism and determining what threats are credible.

Allison Toll, also an intelligence analyst with the department, said less than half of domestic terrorism attacks on American soil carried out over the past year were inspired by a foreign terrorism organization.

"I think a lot of people feel that ISIS is the biggest threat to the United States and its citizens," Paige Schilling, intelligence analyst for the New Jersey Office of Homeland Security and Preparedness, said in the video. "In reality, ISIS poses the same threat as domestic terror groups."

The list of groups New Jersey authorities are keeping their eyes on (see below) includes organizations under the tags of "international terrorism" as well as "domestic terrorism," with each presenting an agenda that they seek to accomplish "by any means necessary," according to the New Jersey Office of Homeland Security and Preparedness.

"Law enforcement has to be aware of groups that are known for extremism and violence," said Marny Requa, a Georgian Court University associate professor of criminal justice. "It doesn't just matter that you have a homegrown terrorist group."

Here is a list of groups being monitored by the Homeland Security Office, which included a description. These are not listed in order of importance:

The fact that the threat has become more diffuse, Requa said, shows "the complexity and the difficulty" involved in trying to identify potential terrorism before it happens.

DOMESTIC TERRORISM

Homegrown Violent Extremists (HVEs) are individuals inspired—as opposed to directed—by a foreign terrorist organization and radicalized in the countries in which they are born, raised, or reside. HVEs pose the highest threat to New Jersey and will remain the most likely and persistent threat this year. In 2015, HVEs demonstrated an ability to operate in New Jersey and throughout the United States while connecting with like-minded individuals online and acting independently from organized terrorist groups. Since late 2014, a variety of radical groups such as the Islamic State of Iraq and Syria (ISIS) and al-Qa'ida in the Arabian Peninsula (AQAP) have encouraged HVEs to attack in their home countries.

Environmental rights extremists view manmade threats to the environment as so severe that violence and property damage are justified to prevent further destruction. Groups such as the Earth Liberation Front (ELF) and Earth First! adopt a "by any means necessary" approach, although violent tactics such as arson are considered a last resort. ELF considers acts of property destruction as "nonviolent" because no human beings or animals are directly targeted.

Militia extremists pose a moderate threat to New Jersey because of fundraising and recruitment efforts in the state, involvement in protests and standoffs across the United States, and their ability to coordinate and organize on a national scale. US militia groups are paramilitary organizations that view the federal government as an existential threat to the rights and freedoms of Americans. They judge armed resistance to be necessary to preserve these rights. Last year, Jon Ritzheimer, a militia member from Phoenix, posted a video of himself brandishing a gun and announcing plans to travel to Islamberg, New York, a predominantly Muslim community in the southern part of the state. Ritzheimer said he would "stop at every mosque along the way" to antagonize and intimidate Muslims. Also, Ritzheimer made threats against Muslim Day at Six Flags Great Adventure in New Jersey. He has since been jailed and charged with a federal felony of conspiracy to impede officers of the U.S.

Sovereign citizens throughout the United States view federal, state, and local governments as illegitimate, lacking the authority to issue or enforce laws. They also assert that they are not subject to questioning or arrest by law enforcement, paying taxes and fines, complying with summonses, or possessing official licenses.

White supremacists are extremists who believe in the inherent superiority of the white race. They seek to establish dominance over non-whites through violence. White supremacist groups continue to demonstrate a propensity for violence, lack of organization, and diverse recruitment methods.

Anti-abortion extremists are individuals or groups who believe abortion is unethical and that violence is justified against people and establishments providing abortion services. Anti-abortion extremists advocate murder, death threats, and other criminal activity, including arson, vandalism, and harassment against women's reproductive healthcare facilities to advance their ideology.

The goal of animal rights extremists is to inflict economic damage on individuals or groups that believe all animals—human and non-human—have equal rights of life and liberty. They are willing to conduct criminal activity to advance this ideology. The threat of violence from animal rights extremists in New Jersey is low because laws passed in recent years are having a deterrent effect and some previously extremist organizations have shifted to public outreach campaigns and nonviolent action to push their political agenda. From 2001-06, there were eight documented cases of animal rights extremism in New Jersey; since that time, none have been reported.

Anarchists

Anarchists are individuals or groups that violently reject contemporary capitalism and all forms of government. They are willing to conduct criminal activity to advance this ideology.

Black Separatists

Black separatists are individuals or groups that seek to establish an independent nation for people of African descent.

INTERNATIONAL TERRORISM

Al-Qa'ida is an Islamic extremist organization founded in 1988 by Usama Bin Ladin and other Arab foreign fighters who fought against the Soviets in Afghanistan in the 1980s. Following the Soviet withdrawal from Afghanistan, al-Qa'ida fought to remove the U.S. military presence from the Middle East, particularly Saudi Arabia. In 1996, Bin Ladin declared war against the United States because of its presence in the Gulf region.

Hizballah is an Islamic militant group based in Lebanon and allied with Iran. Its primary goal is the destruction of Israel. Since 2013, Hizballah has plotted attacks against Israeli citizens and institutions in Europe, South America, Southeast Asia, the Middle East and Africa. In January, five Palestinians were arrested on suspicion of joining a Hizballah cell and planning a suicide bombing and shooting in the West Bank. In June 2015, a Hizballah member pled guilty to acquiring nine tons of ammonium nitrate in Cyprus, which was intended for attacks against Israelis.

Since declaring its so-called "caliphate" in 2014, the Islamic State of Iraq and Syria (ISIS) has exploited European travel laws, organized teams of returning European foreign fighters, and radicalized individuals already in Europe to conduct multi-operative attacks. This capability limits law enforcement's ability to detect and interdict attacks such as in Paris last November and in Brussels in March.

Al-Shabaab

Al-Shabaab is an Islamic extremist organization seeking to establish an austere version of Islam in Somalia. In addition to Somalia, the group operates in Kenya, Ethiopia, and Tanzania.

Boko Haram

Boko Haram is an Islamic extremist organization based in northeastern Nigeria, which pledged allegiance to ISIS in March 2015.

Lashkar-e-Tayyiba (LeT)

LeT is an Islamic extremist organization focused on attacking and expelling Indians from Kashmir, a northern state in India that borders Pakistan and is home to a Muslim-majority population.

Tehrik-e-Taliban Pakistan (TTP)

TTP is an Islamic extremist organization seeking to overthrow Pakistan's government and expel US forces from Afghanistan.