BURKE COUNTY, N.C. (WBTV) – A man convicted of attempting terrorism in support of ISIS has pleaded guilty to the murder of a Burke County man as a practice for a mass attack he had planned.

Justin Sullivan was in court Monday morning and plead guilty to first-degree murder of his neighbor, 74-year-old John Bailey Clark. He was sentenced to life without parole for the murder.

The FBI says Sullivan shot and robbed Clark to get money to help him buy an assault rifle he planned to use to commit the mass murder. He used a rifle he stole from his dad’s gun cabinet, which he hid in the crawl space.

WBTV has learned that Sullivan’s case is the first murder in the name of ISIS on American soil.

Sullivan was already serving a life sentence for terrorism, he was sentenced in Burke County last month.

Sullivan pleaded guilty last year. He was arrested on June 19, 2015, and charged with attempting to provide material support to ISIL, transporting and receiving a silencer in interstate commerce with intent to commit a felony and receipt and possession of an unregistered silencer, identified by serial number.

“Those who committed terrorism are not martyrs, they are criminals,” the judge said in Tuesday’s sentence hearing in Asheville.

Sullivan, who called himself The Mujahid in his contacts with the Islamic State, is accused of plotting a mass killing in support of ISIL.

“As alleged in the complaint, the defendant was planning assassinations and violent attacks in the United States and is charged with attempting to provide material support to ISIL and federal firearms violations,” said Assistant Attorney General Carlin. “The National Security Division’s highest priority is counter-terrorism and we will continue to pursue justice against those who seek to provide material support to designated foreign terrorist organizations.”

According to a criminal complaint, the FBI became aware of Sullivan’s plans to obtain a semi-automatic AR-15 rifle at the Hickory Gun Show in Hickory on June 20, 2015, “which he planned to use to kill a large number of U.S. citizens on behalf of ISIL,” court documents state.

An undercover FBI agent then made contact with Sullivan.

“My highest priority is to detect and prosecute violent extremists and protect innocent Americans from terrorist attacks,” said Acting U.S. Attorney Rose.

Sullivan admitted that he attempted to commit terrorist attacks against innocent people in North Carolina and Virginia, court documents state.

In filed plea documents, Sullivan admitted that he took the following steps towards carrying out terrorist attacks in North Carolina and Virginia:

Recruiting the UCE

Obtaining a silencer from the UCE

Procuring the money that would have enabled him to purchase the AR-15

Trying to obtain a specific type of ammunition that he believed would be the most “deadly”

Identifying separate gun shows where he and the UCE could purchase AR-15s

Obtained coupons for the gun shows he planned for himself and the UCE to attend on June 20 or 21, 2015.

Last month, Assistant US Attorney Mike Savage called the killing of John Bailey Clark just a few doors down from Sullivan’s home a “Cold blooded killing.”Copyright 2017 WBTV. All rights reserved