Assaad al-Haj Ali Ibrahim is the uncle of Mohammad Youssuf Abdulazeez, 24, who killed four US marines and a sailor at two military centres in Chattanooga last week, before dying himself in a shootout with police.
Intelligence services "released my client, university teacher Assaad al-Haj Ali Ibrahim, who has been held since last Friday," Abdelkader al-Khatib told AFP.
He is in "good health, but tired" after being interrogated by the FBI and Jordanian intelligence, and is now back with his family, the lawyer added.
Abdulazeez stayed with his uncle and worked in his mobile telephone shop during a visit to Jordan lasting several months last year.
Khatib said US authorities were interested in knowing more about that visit to better understand the gunman's state of mind before he went on the deadly rampage.
Abdulazeez was born in Kuwait to Palestinian parents, according to Jordanian authorities. He does not have Jordanian nationality despite being given a Jordanian travel document in 2014 -- a common practice with Palestinians -- they added.
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