The person believed responsible for an attack targeting a Palm Springs fertility clinic Saturday posted rambling online writings before an explosion that investigators are treating as an act of terrorism, a law enforcement official told The Associated Press.

“Make no mistake: This is an intentional act of terrorism,” Akil Davis, the head of the FBI’s Los Angeles field office, told an evening news conference.

Law enforcement sources told CBS that the Bartkus, the suspect, is a resident of Twentynine Palms, home to a large marine base about an hour away from Palm Springs.