some thoughts
sticking with the GB4 on this
seems more than likely all 4 were identified online based on the fact that most were out of state, recently moved or were in transition. possible to argue against, but it is more than likely this is how they were identified. thus, LISK has a computer. More importantly he also knows about attribution. Police were not able to link any suspects through this internet usage, despite their attempts. (Didn't they confiscate someone's computer/laptop for this purpose)? He more than likely cased Craigslist or back page, perhaps through VPN even, found someone he like and took down their phone number. he then called from a burner away from his location of residence. every fishing attempt could not have been successful. those interested or desperate he groomed over the phone via multiple calls (see Costello).
he used burner phones. again, no attribution on these despite police attempts to investigate. these burner numbers were easily identifiable through phone records and using them at any time left a trace (date, time, location). IMEI records would lead back to when/where the phone was purchased, which means LISK purchased in cash and likely in some disguise to account for cameras. I feel quite certain the police have already followed this line of investigation. would also venture to guess he never turned them on at or near his home, otherwise police would have been able to zero in on his location using basic correlation. one victim, one phone. what about those he contacted that didn't agree to his terms? re-use that same phone or ditch it? I would guess he ditched it.
he paid attention to cameras and/or positioned himself out of line-of-sight of possible witnesses. Possible he cased each initial contact location using online maps and then in person. the hotel on LI, for example, is right off a major thoroughfare with easy ingress/egress. these parameters are easily searchable online, even 15yrs ago. his ability to remain out of camera angle at contact-point, however, shows his knowledge of their existence. At the house in Babylon, again he knew right where to park. Not necessary to be local to do this. its simple internet & street casing. he was deliberate and this takes time & preparation.
his use (and non-use) of victims phones. picking high traffic and/or remote areas when using these, such as Times Square & Fire Island. This points to intentional obfuscation and non-attribution. Just like Times Square, the Fire Island ping was something he needed or wanted to do, but was carried out in such a way as to point away from him. wondering what he did with those victims who brought along their phones. Did he ask them to turn it off? He had to have at some point, otherwise this would have revealed his victim's location based off tower pings, right? Melissa seems like the only one who we know for certain did this. Megan & Amber left theirs behind and Maureen told her friends she was robbed, although she was still able to make calls and had enough money to go home.
Did these girls know him or had they met him multiple times before? Doubtful. Any contact with a potential victim increase the chances of being caught. It doesn't seem like he likes to take chances like that. If he did meet any of these girls more than once, he'd have to manage the phone-attribution situation multiple times, requesting they leave it behind or having them turn it off & take the battery out. Asking someone to do that is super weird and if you let them go, they will definitely talk about it. In Maureen's case, there is a higher interest in her 'regular' contacts due to her Craigslist page being blocked. These 'regulars,' however, were almost certainly interviewed by police.
the dump site. when you look online, it's the only section of road on jones beach island that has a long and sizeable section of center median. meaning at night even on-coming traffic would not really be able to see. if you're looking to dump a body, this location would seem like a place to go & investigate. find it online, case it in-person later. like everything else he's done, I would venture to guess that this location was identified in such a way as to point away from him or at least not point back to him. Point being, you don't have to be from LI to have identified Gilgo as a good dumping ground. Also, why dump multiple bodies so close to where someone just went missing, for example? Even if the dump site was selected & used pre-Gilbert, he still dumped 2 bodies there after that case broke. He was either confident in their concealment or put them there knowing they might be found. Gilbert has certainly inserted much confusion into this case, I think everyone would agree.
so how to find him? phone data aggregation and perhaps web address IP logs? cross referencing these might reveal a known phone usage corresponding to webpage access. he visits a page, then activates a phone around the same time. a big stretch, I think, and totally moot if he used a vpn. and besides, only way to do this would be if police still have access to the historical data (I understand they might). or maybe mapping all known burner usage to identify geo location trends? maybe he did get lazy and call from near his house on multiple occasions.
we know he has a car, has a computer, has extra money to buy phones, appears more tech savvy than the average Joe, especially for the late 2000's, has some time on his hands AND local to the NYC/Long Island area (for summers at least). AND maybe he has the initials HM or WH or whatever. Pick-ups were in Manhattan, Bronx and LI, with a dump site on the beach. his ability to avoid detection while using electronics shows he knows a lot about police investigative methods. either experience in or a huge fan of police/military or other law enforcement, etc. there is much to complain about in the police, however, I think it's important to realize & understand the degree to which this guy is organized and diabolical.