3 Covering Saint Johns County, where we've seen an alarming number of hit-and-run crashes in the area. Tonight, we're getting a closer look at just how difficult it can be for investigators to crack these cases. What you see here is scene video from four deadly hit-and-run crashes, still unsolved. There have been a total of 6 in Saint Johns County, since 2011. Channel 4's Vic Micolucci spoke to a lead detective about the work that goes into these investigations. He joins us now live... Vic? 3 It's certainly not easy...they could take months ... or years to solve. But deputies say these cases are not cold, clues are still coming in, and they need your help to finish the job. 00-06 18-22 00:42 and impact with the vehicle this size, anything here, the plastic fiberglass, all of this is subject coming off. Deputy Joseph McGinnis is a crash reconstruction expert with the St.Johns County Sheriff's Office...he's also the lead detective on 3 deadly hit and run crashes that the sheriff's office is investigating.50:25 all three are yet to be solved but we are still working evidence in each of the cases. 50:57 hit and run crashes or a unique challenge just because of the lack of witnesses at the scene. But when these crashes do occur you have a lot of physical evidence in most cases that give us an opportunity to follow up. Our records show there have been 6 unsolved deadly hit and runs in St. Johns County since April 2011... 3 are in the sheriff's office's jurisdiction...the others worked by St.Augustine police and the highway patrol. McGinnis says it's not easy because most of these happen at night ...and the only witnesses are the driver and the person who was killed. That's why he pairs autopsies with evidence at the scene...then looks for cars or trucks that could have that kind of damage. 02:57 if the car were to hit me this kind of an orientation, I'm going to come up and and up on top of the hood. You will see dents on top of the hood. And I could possibly go up to the windshield. If it's more of a glancing blow on this and here, you're not going to see me go up as much over the hood, at all but you're going to see me , More along the line and impact this is what we call in a a-pillar right here or the plastic mirrors will come right off as well. McGinnis says he and the other detectives will never give up...finding justice for those who were left behind...people like Bryan Wrigley, Haley Smith and most recently Stephon Sweet. But he says he needs your help in piecing together the sometimes very intricate puzzles... 52:16 in many cases you have a driver who may not even realize that they struck a person. So it's just a matter of just trying to talk with people in the area to see if they recognize a vehicle that came through the area at that time. McGinnis says neighbors can keep an eye out for people who have body damage to their cars without any reason...or maybe made some quick repairs...he says also look for changes in behavior.He says if you even think you have useful information, call crime stoppers or deputies. Vic, is there any reason to believe these hit and runs may be related?