Pastor Rick Warren said Thursday that his son, Matthew, purchased an unregistered gun over the Internet. It was that weapon that he used to take his own life last week after years of battling mental illness. "Someone on the internet sold Matthew an unregistered gun. I pray he seeks God's forgiveness. I forgive him. #MATTHEW 6:15," Warren tweeted Thursday. The Orange County Sheriff's Department told the Associated Press it is trying to identify the seller, but the gun's serial number was unreadable, making it difficult to trace the firearm.