Someone who does crime together with you is your accomplice in crime. It's best to "take care of" these before the coppers get to him/her.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
The accomplice was indeed like a bug that flew into the fire in summer.
There is high probability that the accomplice has already fled the country.
He was a really wonderful criminal who could easily get out of the most dangerous situations by himself. He boasted that he would never need an accomplice.