aid and abet, to

To assist someone, usually in a mischievous or illegal activity. Gary was arrested and charged with aiding and abetting the jewelry thief. I know other kids aided and abetted Paul in egging our house—he's just the only one who got caught.

Cliché to help someone; to incite someone to do something, possibly something that is wrong. (Originally a legal phrase.) He was scolded for aiding and abetting the boys who were fighting.

If someone aids and abets another person, they help or encourage them to do something criminal or wrong. His wife was sentenced to seven years imprisonment for aiding and abetting him. Note: This expression is often used in legal contexts.

To assist and promote or encourage something or someone. The pairing of these nearly synonymous verbs, always in this order, comes from criminal law, where it denotes helping, facilitating and promoting the commission of a crime. The verbs themselves are quite old, aid dating from about 1400 and abet from about 1300. Although the term still is principally used in relation to criminal actions, it gradually crept into more general speech, as in “The influx of Canada geese on the golf course, aided and abetted by people feeding them . . .”