A murder case 1

Lets say, you a detective and now you're met with another case. A girl was found dead near a building still under construction. It is said that she committed suicide , but of course that is not the case. The worker who found the body gave you a look at the scene." this is what is left of her... sad you know, i heard she's doing good in school..." said the worker.
"Hm.... could you show me where she might have jumped of from?"You said.
Without hesitation the worker brought you up to the second top level of the building. He had to pull open the close door to get to the "outside"(it was still under construction so its still exposed). There was still no handle on door from the "outside", so it was slightly left open.
Not far you saw her bag, everything was still in contact. From this height you're standing, a fall is definitely fatal."Why did see jump... or did she jump?"You said yourself. Another worker came up to you and said," I was the person who first saw this body... went up to all levels to check, found out that the door at this level is shut. So i went to check, turn out she jumped from here."
You asked him," Are you sure that what you told me is correct." He replied," Ya, very sure of each detailed, everything! I'm very sure! She must have jumped."
"I guessed this isn't as simple as it seems... She didn't jump, someone pushed her!" You said.

So can you proof it?