MONTREAL - Following a deluge of thousands of complaints from around the world, Montreal police have launched an investigation into a St. Laurent man accused of making hundreds, if not thousands of deadly threats.

The man is believed to be Dennis Markuze, but uses a variety of pseudonyms when online, including David Mabus and Hebert Marxuxe.

Complainants say that he creates accounts on Twitter or on message boards then starts insulting, harassing, and threatening atheists, scientists, and journalists with profanity-laden messages telling people that they will be executed and subjected to the judgement of God.

In October 2010 Markuze showed up at the Atheist Alliance International conference in Montreal, where he was recognized and challenged by attendees before he left.

Someone identifying themselves as Markuze then went online to the Humanist Canada website and wrote: "believe me, the only reason the photo is available is because I WANTED IT OUT THERE.... actually it is quite a flattering photo of me: With finger cocked and pointing, I say "And I gotta take out these idiots!"

Many people say they have complained to the Montreal police department in the past few years but that no investigation was ever launched.

Police have said that any investigation would be difficult because while Markuze lives in Montreal, many of his alleged victims live in other countries.

That changed this week, when more than 3,000 people signed a petition calling on police to investigate reports of death threats. Each signature resulted in an email to police.

Kyle VanderBeek, a San Francisco man who started the petition, says the threats are disconcerting and he wanted to act now instead of waiting for things to escalate.

VanderBeek says while testy exchanges are common online, alleged threats of decapitations, executions and genocide are not.

Montreal police have posted several messages on their own Twitter account, assuring people they are investigating and asking them to stop bombarding police with messages.

With files from the Canadian Press