Please whats the name of this thriller movie?

[Crystal Divinity]

My mother and i were bored the other day and were asking random questions,
Until one question occured about a thriller that she watched ages ago. She says she watched it around 20 years ago, so roughly around the 1990's.

She said (Briefly, from what she can remember) that it was about a father who kills his kids and this man kills many people before anyone would even think it was him. The thing is, no one would ever suspect a thing from him because he acts so angelic and he seems to harmless to be a killer, he is so good at hiding what he's doing that the thought of him being a killer would have never crossed anyones mind. Then people start thinking that the children died of natural causes because of the way he killed them and planned out where to dispose their bodies

Anyway, as time goes a police officer gets involved and uses a light that detects any hidden blood stains which finally uncover that he is the murderer.

My mum is going insane because she can't stop thinking about the movie title, if you have a couple titles in your mind, list them all out and i would do my homework on them. Thanks guys.

[moviefreak]

There is a movie called 'In A Child's Name' (1991) where a man murdered his wife and nearly got away with it until they sprayed chemicals that made the blood glow. There were glowing bloodstains all over the bedroom and down the stairs. Could that be the one she meant?

[Jake Shahriari]

Step Father? the really old one? sorry, i watch a lot of scary movies, but im 14 and i was not alive in the time that movie was born. that might be right though