Rick Warren’s son Matthew shot and killed himself with an unregistered gun, the pastor and police confirmed Thursday. “Someone on the Internet sold Matthew an unregistered gun,” Warren wrote on Twitter. “I pray he seeks God’s forgiveness. I forgive him.” A spokesman for the Orange County Sheriff’s Department said it was impossible to tell if the gun was registered, because the serial number had been scratched off, which is against federal law. Matthew Warren, 27, the son of megachurch pastor and The Purpose Driven Life author Rick Warren, shot and killed himself Saturday.