Who Did It?

Did you ever watch a tv mystery and know "who did it" before the plot thickened? I must be watching too much tv lately, or it's an accumulation of a lifetime of watching tv. Mom says it's time to write my own mystery. Are the stories simple, or am I becoming a sleuth? I long for a mystery where I have no idea who commited the crime or why they did it. I guess that the writers follow some sort of a formula when writing. The formula needs to be changed.