i Register
In some senses, culprit is marked as UK. Watch for register when choosing this word.
ADJ
big, chief, main, major, prime, real, worst
Lack of exercise turned out to be the main culprit behind his weight gain over the years.
likely, obvious
VERB + CULPRIT
hunt
Detectives are still hunting the culprit responsible for the store robbery last month.
apprehend, catch, identify, find, track down