He wrote the story with his friend's 'assistance'. = He wrote the story 'with the assistance of' his friend. [=his friend helped him to write the story]
Our family had to 'go on public assistance' [=receive money from the government] when my parents lost their jobs.
Nobody 'came to her assistance' [=nobody helped her] when her car broke down.
(..) you up in the middle of the night. You should. We invented for you a fictitious companion named Tarpon so that you could use some information and assistance, which you can get from a retired cop named Haymann. That same Haymann prefers to keep in the background. Yes, but... (..)1981 To Kill a Cop