Is there any good reason to think Sid Vicious didn't kill Nancy Spungen?

I’m not an expert on the Sex Pistols. My understanding of the tragic end of Sid and Nancy pretty much matched what Wikipedia says:

However, I recently read Legs McNeil’s Please Kill Me: An Uncensored Oral History of Punk. And in there, a couple of people don’t believe that Sid could possibly have killed Nancy, 'cause he loved her so much and was such a gentle guy. Someone (and I don’t have the book handy, or I’d have a name to connect to this story) believes that Nancy got into an argument with a drug dealer while Sid was unconscious, and that this dealer killed her and took off. The murder was pinned on Sid, who didn’t really remember what happened, and once Sid died any other lines of investigation were dropped.

Now, I realized that we’ll probably never know what exactly happened. But is there any good reason to think that someone other than Sid killed Nancy? Or is this more than likely hopeful speculation by people who liked Sid and don’t want him to have done it? Please Kill Me is interesting, but completely driven by interviews, so there’s no reference to any other reports, theories, avenues of investigation, or anything else.

From Court TV’s Crime Library: Sid Vicious & Nancy Spungen:

Like the time he gently hit an audience member with his bass, or the time he gently beat that music writer with a chain…

I’ve read Deborah Spungen’s “And I Don’t Want to Live This Life.” Granted, ishe’s Nancy’s mother, but it’s an interesting read. She says Nancy wanted to die, and she could see where Nancy would buy the knife and tell Sid “If you really love me, you’ll do anything for me, including kill me.”

Sid was abusive to her, and apparently had a mean temper.

I should note that evaluations of Sid’s character are paraphrases of what friends said about him, not my own opinions.

So was the Steve C theory investigated by (and presumably discarded by) the police, or is that a theory that’s come up in the years since the case was closed?

The theory was floating around a the time of Nancy’s murder. It was thought of by Sid’s manager, and later dismissed. Wtih Sid’s suicide, the cthe murder investigation was closed.