Could it be Shadow of a Doubt by William Jeremiah Coughlin? That was published in the early '90s, had an alcoholic down-and-out lawyer with a client accused of murder. Seems to be his first novel. I haven't read it, so I don't know if there's a motorcycle gang, but take a look:
http://search.barnesandnoble.com/Sha...?itm=10&usri=1
or
http://www.fantasticfiction.co.uk/c/...w-of-doubt.htm
If that's not it...
Okay, you're certain this was the author's first book. Do you happen to know if the author later wrote other books? Did it maybe become the first in a series?
Would you classify this as a legal thriller, mystery, slice-of-life, literary, mainstream or some other genre? It is fiction, a novel, right?
You read it in the early '90s. Was it fairly new/recently published then, or might it have been published in the '80s, '70s or before that?