Pat Tillman's Brother Battling Mental Health Issues Prior To Arrest, Family Says

Richard Tillman, the brother of American hero and former NFL player Pat Tillman, had been battling mental health issues prior to his arrest over the weekend, his family said in a statement on Monday.

Richard, 44, was taken into custody in San Jose, Calif. on Sunday morning ... after authorities alleged he caused a massive blaze at a U.S. Post Office by driving his car into it.

He's currently being held at a Santa Clara County Jail on a charge of arson.

Kevin Tillman, Richard's brother, commented on the situation to NBC Bay Area ... revealing Richard "has been battling severe mental health issues for many years."

"He has been livestreaming, what I’ll call, his altered self on social media for anyone to witness," Kevin said. "Unfortunately, securing the proper care and support for him has proven incredibly difficult -- or rather, impossible. As a result, none of this is as shocking as it should be."

Authorities say "the motive and circumstances" over Sunday's crash are still being investigated by detectives.