Garak was under the influence of drugs which he did not choose to take, therefore no, he is not guilty of murder in the Empok Nor cases.
On the other hand, if he had chosen to take them, then he would be guilty of murder.
That's a VERY good point about the fact that Garak didn't choose to take that drug. He didn't know what it was when he stuck his fingers in it. He wasn't the equivalent of a drunk driver, who knowingly got drunk and would therefore be liable
for reckless disregard for life if he killed someone.