Frailty (2002)

The story follows an FBI investigation in present day Texas. Fenton Meiks, a young man, approaches the lead FBI investigator, claiming he knows the identity of a serial killer who calls himself "God's Hands." The FBI agent is curious, but unimpressed until Fenton reveals that the killer is his younger brother Adam. Fenton recounts in a series of flashbacks, how he and his brother grew up in a very loving family, raised by their widowed father. All that changed, the day his father awoke, believing he had been visited by an angel and given a mission to destroy "demons" - seemingly normal looking people, who walked this earth as pure evil. Fenton's father, and then his brother Adam, swore to carry out this 'divine' mission. Fenton refused to participate in the killings. Out of loyalty however, he refused to go to the police, until now. The FBI agent follows Fenton to the family's rose garden only to be surprised that neither evil nor innocence are what they seem.