One woman still had a voicemail from the alleged serial killer - the message was obtained exclusively by Eyewitness News.
"I assumed he just wanted to do some work together, but he always made me a little bit uncomfortable," said Dominique Vidal.
Vidal says Heuermann left her the message in late February when she left a networking group for architects and designers she says they were both in.
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Heuermann was apparently in the group up until his arrest on Thursday.
Vidal is now recalling some of their - now chilling - past conversations.
"He asked me if I knew about the Gilgo Beach murders. And back then I will say 'Oh you know, he's just from the area, maybe you know, he's just a local talking about and would think that I'd find it interesting.' But now I see it as a serial killer," Vidal said.
Eyewitness News learned Saturday night that investigators spent the day searching his house filled with old apparent mementos. They will see if there are any trophies from the victims.
Law enforcement now has a full DNA sample, which they can now use to determine if he is linked to any further murders.
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Cassandra Wickert had spoken to Heuermann when he was just her neighbor in Massapequa Park.
"He talked to us about how he does woodworking and building furniture, and his father used to build furniture," said Wickert.
Investigators say Heuermann's obsessive web searches about the case, his use of burner phones, and DNA extracted from pizza crust helped tie him to the murders of three women and made him a prime suspect for a fourth woman.
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Sources say authorities had to make an arrest Thursday night knowing he was still interacting with sex workers.
Heuermann's possible link to some of the other Gilgo Beach deaths remains very much under investigation.
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