Looking for an apocalypse-themed anime

I'm looking for an anime series (I guess it could have been a movie, but I think it was a series) that I saw on TV many years ago. It couldn't have aired any later than 2002, because I saw it while living in a house that I moved away from in July of that year. So it would most likely be something made around then, maybe late 90s at the earliest (bearing in mind that just because it aired in a particular year doesn't mean it was made in that year). It would be an anime that aired in the US, on Cartoon Network, and was of course dubbed into English.

The details are very fuzzy in my memory, since it was such a long time ago. But it was some sort of apocalypse-themed series, and I believe it involved someone deliberately releasing a virus to destroy humankind. That's how I remember it, but it could have been via different means; the main thing is that someone deliberately set out to wipe out humanity, perhaps because they deemed the world to be too corrupt or something. There may have been some religious themes, but I can't be sure about that.

The only concrete thing I remember is that there was a scene in which the person who seemed to be responsible for this apocalypse was killed by a person who was trying to stop him. They had a verbal confrontation in which he calmly justified his actions, and then he was killed, with a gun or blade I don't remember, but I think it was a blade. This doesn't seem to have been a show about super-powered people or anything supernatural as many anime are. The setting was modern, possibly futuristic but probably not very much. The art was "realistic" looking, like in Death Note for example, i.e., I don't think the characters had wacky hair or outlandish clothes or anything.

Sorry for a slight shortage of details. This was a show that I only saw a little bit of, and it was a long time ago, at least 15 years. There's something about it that made an impression on me and has always stuck in my memory, and in the back of my mind I've always wanted to see it again and find out what happened. Any help in finding it would be appreciated.