((make)) an error ((in)); a mistake ((about, in))
make a gross [slight] mistake／commit a gross [slight] error
He admitted that 「it was his fault [he was to blame].
There is no way of telling whether that killing was accidental or intentional.
過失傷害(罪)｜accidental [unintentional] infliction of injury
過失致死(罪)｜(an) accidental homicide; (an) involuntary manslaughter
He was arrested on suspicion of professional negligence resulting in death.