BD tells Le that SA isn't there, and THEN consents to have them search her home?? And they find him there? And execute the warrant on him.
What the sam hill was she thinking???
http://www.reporternews.com/news/2011/mar/18/mother-missing-colorado-city-teen-hailey-dunn-arra/
Either that he would HIDE, or that he would NOT HIDE, and it would not be a big deal that she had lied "for a minute." I seriously doubt she thought she could (and would) be ARRESTED for it.
Now... since search warrants were being executed at the homes of Shawn's mom and grandmother, they had probably ALSO been asked if Shawn was there because they had a warrant to search his person. At some point, there was contact between Shawn and someone who shared this information with him. He didn't WANT to be "searched" and the available information about the warrant was vague enough that he didn't know specifically what they were looking FOR.
He'd certainly have been bright enough to get rid of anything incriminating (related or not to the CP or Hailey, including drugs or weapons) he was carrying, as he knew an encounter with LE was inevitable, and that his body would, in some way, be examined. He also high-tailed it over to Billie's, where he probably WASN'T welcome, both because she didn't want LE coming to HER house to see him, and because, as she had recently indicated, their relationship was over. He may have figured this was a good place to lie low, since Billie had been quite vocal in her disgust with him over the cheating, the child











, and whatever other information she had gleaned from LE. He figured nobody would look for him in a place he was known to be unwanted.
The point here is that, like us, they did not know what a "body warrant" might entail, and whether it was to look for distinguishing characteristics not generally visible to the public or to collect bodily fluids and hair.
Did Shawn know what they were looking for and ditch it?
If not, what did he THINK they were looking for?
And why would he not want to comply?
If he had figured out that it was the "thing he usually carries but wasn't" (either because he had cached it somewhere in response to the ongoing searches, discarded it previously, or just happened not to have it that day) it would have been an easy thing to ditch it if he hadn't already and (appear to) cooperate with LE. I don't think he knew it was for something he could "take off" or ""put away." He either thought they had photos they were trying to compare to him, or physical evidence (beyond hair, which could be transferred among people living in the same home), like DNA.