The message might not have sent due to bad signal.
He may have written the message days before when he was feeling suicidal but didn't send to not alert the family. Later on he killed himself impulsively. Anywhere from one-third to 80% of all suicide attempts are impulsive acts, according to The New England Journal of Medicine. 24% of those who made near-lethal suicide attempts decided to kill themselves less than five minutes before the attempt, and 70% made the decision within an hour of the attempt. [1].
My guess would be that he knew that sending an SMS will to his brother would cause his brother to reach out to him.. a conversation he'd rather just avoid since he seems like his mind was made up.
