No foul play was suspected, and though few details have been released, police say the athlete appears to have died from a self-inflicted gunshot wound to the chest.
"Life-saving efforts were performed, however they were not successful," said Oceanside Police Chief Frank McCoy, reports NBC LA. "This case at this point is being investigated as a suicide," McCoy continued.
His mother Luisa Seau said she was in church when she heard the news, "I pray to God, 'Take me, take me, leave my son.' But it's too late," she told reporters at an impromptu press conference.
A neighbor said he saw Seau smiling and happy and playing the ukulele on his balcony just two days ago, notes the L.A. Times.