A New York architect accused of murdering three women and dumping their bodies near Gilgo Beach on Long Island allegedly made “taunting” calls to a relative of one of his victims, prosecutors say. Rex Heuermann, 59, was arrested on Thursday and charged with six counts of murder in connection with three of 11 unsolved killings known as the Gilgo Beach murders. Suffolk County district attorney Raymond Tierney wrote in a court filing that the sister of victim Melissa Barthelemy received “taunting calls” near to Mr Heuermann’s office in Midtown Manhattan after her disappearance in July 2009. Mr Heuerman also used the phones of Barthelemy and another victim Maureen Brainard-Barnes to check their voicemails after they disappeared, the district attorney wrote while requesting the suspect be held without bail. Mr Heuerman has been charged with first and second-degree murders of sex workers Barthelemy, 24, Megan Waterman, 22; and Amber Costello, 27, and is considered a “prime suspect” in the murder of Brainard-Barnes, 25. Mr Tierney added that investigators found “no instance” where Mr Heuermann was in a different location from where the womens’ cellphones had been used. During a court appearance on Friday, Mr Heuermann pleaded not guilty to all charges. The bail application detailed disturbing internet search records traced to one of Mr Heuerman’s burner cellphones for “sadistic, torture-related pornography” and child pornography. Investigators say Mr Heuermann also looked up images of the victims and their relatives, and conducted “counter-surveillance” on the criminal investigation on his burner phone. The searches included “why could law enforcement not trace the calls made by the long island serial killer”, and “why hasn’t the long island serial killer been caught”. Mr Heuermann allegedly created an email account under the fictitious name Thomas Hawk, and used it to “repeatedly view hundreds of images depicting the murdered victims and members of their immediate families”. He also used the account to search for podcasts and documentaries about this investigation. Mr Heumann was observed by law enforcement purchasing credit for one of the burners at a cell phone store in Midtown. He used the phones to solicit the services of sex workers and create fake Tinder profiles, authorities say. Law enforcement first identified Mr Heuermann as a suspect in March after his Chevrolet Avalanche was linked to a witness sighting during Costello’s disappearance. Subpoenas and search warrants uncovered records of burner cellphones used to arrange meetings with three of the four victims before they went missing. District Attorney Tierney said the weight of evidence against Mr Heuermann meant that the “only means to ensure (his) return to court is to remand him without bail”. Mr Heuermann, a married father of two, lives in Massapequa Park, near where the victims disappeared from. Read More Rex Heuermann charged with three Gilgo Beach murders as burner phones and truck tie him to serial killings Gilgo Beach murders – live: Long Island serial killer suspect Rex Heuermann charged with killing three Manhattan architect, family man and accused serial killer: Who is Gilgo Beach suspect Rex Heuermann?