The suspect/perp is a Shiite, and the terrorist group was/is supported by Iran. PERIOD.
http://foreignpolicy.com/2015/09/08/saudi-arabia-khobar-hezbollah-iran/
Did Iran Give Up the Khobar Towers Terrorist?
It sure looks like it. And that signals an interesting change in Iran’s post-nuclear deal relations with America.
By Ali Soufan
September 8, 2015
[Ali Soufan is a former FBI Special Agent who investigated and supervised highly sensitive and complex international terrorism cases, including the East Africa embassy bombings, the attack on the USS Cole, and the events surrounding 9/11. He is the author of The Black Banners: The Inside Story of 9/11 and the War Against al Qaeda.]
[snip] A Shiite born in al-Qatif, Saudi Arabia, in 1967, he was a state-sponsored and then state-sheltered terrorist — the “state,” in each case, being Iran, working with its proxy Hezbollah. The bombing of Khobar Towers, which killed 19 U.S. Air Force personnel enforcing a no-fly zone over parts of Iraq and wounded hundreds of others, involved actors in four countries — Saudi Arabia, Iran, Lebanon, and Syria — working with the Iranian-supported Lebanese Hezbollah and the Iranian-supported, but Saudi Arabia-based, Hezbollah al-Hejaz (a separate group from the Lebanese Hezbollah but still ideologically aligned with them and Iran). After parking a massive truck bomb near the tower’s housing complex, Mughassil left the scene, remotely detonated the bomb with an explosive yield of 20,000 pounds of TNT-equivalent explosives, and fled to Iran, beyond the reach of U.S. and Saudi security and intelligence services. [/snip]
The attack was carried out under the direction of Iranian Revolutionary Guard General Soleimani, who thanks to Trump, has assumed room temperature.