In missing persons cases, there are many civilian volunteers that assist local and state SAR teams. Many times, it's initially unclear whether the missing person is a victim of foul play, injured and unable to signal for help, or simply lost. It's the job of law enforcement officials, working with volunteers, to collect clues and determine exactly what the mission will entail.
SAR teams' first priority is to establish a search area. This is typically a circle based on the last place the missing person was seen. As the search progresses, that point will change -- for example, if an article of clothing is found along a trail. This point then becomes the last known position, or LKP. If you have a last point seen and a last known position, then you have a reasonable approximation on which direction and how fast the person was traveling. For instance, if a woman was spotted at a trailhead at noon, and her water bottle was found on the trail an hour later four miles north of the trailhead, then you can hazard a guess that she's traveling north at about four miles an hour. This helps to establish the search area.
When it comes to techniques, each type has its own probability of success. A slow and thorough search may produce more clues, but if time is of the essence, it may not be the best way to go. It's generally thought that multiple fast searches are more productive than a slower and more thorough approach. A hasty search team is typically the first to be deployed. Team members either work for the sheriff's department or are citizens who have undergone a great deal of SAR training. Their job is to pair up and move quickly -- the goal is to scan high-probability areas and end the search as soon as possible.
A grid search team moves slower and more methodically, combing the area with a long line of volunteers. Grid searchers typically find clues that help more experienced SAR teams find the missing person. A choke point is a man-made or geological characteristic that allows the SAR team to narrow the search. For instance, if there's a wide river that's only able to be crossed by bridge, the SAR team will station a lookout person at that bridge and the team can focus elsewhere. Sometimes SAR teams will use track traps to see if a person has passed through a particular area. One trap technique is to bring sand in along a wooded trail and periodically check it for footprints.
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