After looking at that later carefully Allen already knew that it was the same person who sent him this letter. Because previously he noticed a code in the previous letter and now he noticed the same code in this letter.
He instantly did not open that later because right now he was in front of everyone so he could do that later. Samantha and the others were very curious about that letter because they also became surprised when they saw this letter. Why would someone send him later like this?
Sometime later,
After coming back to his room he opened the letter and then read it. Finally he got to know what was written inside of the letter.