The police found he had purchased the weapon in advance, proving it was a premeditated crime.

premeditated 是动词 premeditate 的过去分词形式，在句中作形容词使用。premeditate 由前缀 pre-（表示"预先"）和动词 meditate（"思考、谋划"）组成，字面意思是"预先谋划"。 premeditated crime 指"经过事先谋划的犯罪行为"，即"预谋犯罪"。