The head of the popular Saddleback Church in Orange County took to his Twitter account on Thursday, saying he forgives whoever sold the weapon to his 27-year-old son Matthew, who committed suicide last Friday.
The Orange County Sheriff's Department said the weapon's serial number was scratched off, making it impossible to trace.
Rick Warren and his wife, Kay, said in an email on Saturday that their son struggled for much of his life with severe depression and suicidal thoughts.
Warren founded Saddleback Church in 1980, according to his biography on the church website, and over the years watched it grow to 20,000 members. He and his wife began by holding Bible studies for people who weren't regular churchgoers.
Matthew was the youngest of their three children.
The pastor has tweeted daily since his son's death, including posts about seeing his son's body at the coroner's office for the first time, combating the stigma of mental illness and the challenges of grieving when a public figure.
The Associated Press contributed to this report.