What do you mean? I just assumed that they took it to look for strange DNA. (Although I don't understand why they didn't take it on day 1).
Actually, I don't understand a lot about the first days. I don't understand why every inch of the house was not fingerprinted. Why every piece of bedding and toy in the crib was not collected. I'm glad they eventually picked the stuff up, but why the delay? Were they working from the assumption that the parents did "it", and later realized that the parents may be innocent?
That is probably why they took it. Still would like to know what was inside or had been inside the Gloworm.