Electronic devices belonging to Mohammad Youssuf Abdulazeez, the gunman killed four Marines in attacks on military centers in Chattanooga, Tennessee, have been sent to the FBI crime lab in Virginia for analysis.
Authorities have not uncovered evidence that the shootings were inspired or directed by ISIS or any other terror group. "He doesn't seem to have left much of a social media footprint," one official said.
The FBI is looking into recent blog activity attributed to the gunman. The SITE Intelligence Group said he posted three days before the shooting that "life is short and bitter" and that Muslims should not let "the opportunity to submit to Allah ... pass you by." The blog has not been confirmed by NBC News.
Abdulazeez's father was briefly investigated several years ago for possible connections to a terror organization. But that investigation was closed, and the father was removed from government watch lists.
U.S. officials say the father was briefly in a terror database because he made contributions to a charity connected with a terror group, but it was determined that his interest was strictly charitable, and the case was closed.
U.S. authorities are also looking into a trip to the Middle East last year by Abdulazeez. He left the United States in April, returned in November and traveled through Jordan, where his father is from. Investigators are looking into whether he went to Yemen.
"Jordan doesn't bother us. That's a moderate country. But Yemen would be trouble," one official said Friday.
Investigators say they've heard from his friends that he recently began attending religious services more often and grew a beard.
Abdulazeez was killed on Thursday after spraying dozens of bullets at a military recruiting center, then driving to a Navy-Marine training center seven miles away, where he got out of his car and shot the Marines.