Have you known someone who you later found out was a serial killer?
Yes, he's a mystery wrapped inside a riddle buried in an enigma. His story involved an act of revenge he said. Here's what he said. Over a wet February weekend two people had travelled north west across water then across land to a place that was sacred to him he said. They were harpies dressed as men he said and now they were three he said. One was a murderer, a wolf dressed as a lamb he said. They poured fire and brimstone into this sacred place which was the hearts and minds of all that was dear to this man he said. They corrupted and poisoned the innocents with their brutish and corrupt self serving deviant dogma he said. They thought this man was near his end and weakened he said. But he wasn't he said, his long dark night of the soul was almost at at end he said, he would emerge as does the Phoenix he said. They set themselves up in his sacred place and writhed and squirmed as they spat out their venom he said, they set out how this man should be separated and annihilated under the guise of false witness and false testimony he said as they ran their fingers over a mystery deed he said. But the walls had ears you see and he heard it all he said. He had killed before he said but the taste of their blood would be the sweetest nectar for revenge was the sweetest cup of all, an eye for an eye he said. His plan was to travel south east across water on King Neptunes white horses he said, buried beneath a slippery wet deck laden with the fruits of the ocean he said, incognito he said, untraceable he said. Then he described the moment whereby truth would issue forth from their cold dead eyes as he would watch the life drain from them slowly he said. This wasn't enough he said, there had to be more he said for they were legion. He was to travel north west then he said to a place which was one of the 13 gates of hell he said, a place of celebration at the time of his choice he said, a time and place where Mithras rode out over the earth he said, a place where he would make a final mass burnt sacrifice of their cohorts and acolytes he said, a bonfire of the vanities he said, burn the witch he said, to redeem the slaughtered lamb he said. Nemo me impune lacessit he said. He's out there somewhere. Right now. Waiting for justice to be served. Cold he said, delivered with cold steel he said, for he came from a long line of assassins he said. He had no fear he said. He was born that way he said. When I looked into his eyes I believed him, for the fire in them was incandescent, like the eyes of Acheron they were. There are certain men in this world you should never fuck with you see, real men you see, not harpies bathed in the blood of the innocent. There will be blood.
In winter 1974–75 I was taking time off from college to earn money. I was a carpenter in Alberta Canada and when laid off went to stay with a friend from NY who was separated from his wife in Spokane. We went bar hopping a lot and there was a rumor going around Washington State about a guy named Ted who was a murderer and who drove a Volkswagen. A few times to get a rise out of a woman we were chatting up (well into a conversation)we would give our name as Ted. Often there would be a shocked reaction. We thought this funny and it was several years later we realized this was a true reference to serial killer Ted Bundy.
Here is a comprehensive list of KNOWN serial killers. There is a lot of data here, but once again, this represents killers who were captured or killed. I have seen reports that, based on similarities in the crimes, the number of actual serial killers that are active may be much higher.