Intentionally and malevolently; not innocently or by accident. The phrase is usually used humorously to mimic legal language. Don't give me that innocent look. You ate the last piece of pie with malice aforethought!

A calculated, premeditated intention to harm or kill. Outside of legal writing, the phrase is often used humorously or sarcastically. During the sentencing, the defendant's lawyers argued that the death penalty should be reserved for those who killed with malice aforethought. Don't give me that innocent look. You ate the last piece of pie with malice aforethought!