The Riddle in the Shapes

Martha just went upward and downward direction so she could see the police working on the case. "Who is the suspect you are looking for?" Martha asked.

The police had no clue, but they were sure they would soon find that out. 

"Maybe you need help from a 3rd-dimensional being," Martha suggested.

One of the police was restless. He then replied, "a 3rd-dimensional being? What do you mean exactly?"

Martha was all-knowing but conversant about the details. "Well, for one, the 3rd-dimensional being would passed through us, first, with the arrival of a fine point but expanded itself to a long line and then goes back again to diminish to a fine point until it disappeared."

"But what can he really do?" The second police asked.

"First, he could see the width of an existing triangle, or a line and count how many of us were exactly here."

The first police asked, "Can he see the rest?"