At fault

 
(PW)

responsible for making errors
He is at fault for all the errors on the computer.

 (MW)

1 : unable to find the scent and continue chase
2 : open to blame : responsible  >

 (usingEnglish)

Something or, more often, someone that is very special to you is the 'apple of your' eye.

 
(thePhraseFinder)

He caused it. It's his fault. It doesn't necessarily mean the person feels guilty.