Here is a mini walkthrough for the crime scene. Let me know if you need any help.
Magnify glass items:
    Film Canister (gym area on green mat under weight machine)
    Jam (shower area on bench)
    Chocolate Crumbs (gym area below red exercise mat)
Gather pieces for trophy, salad tongs, key, golden weight, sink facet, yellow treadmill button, knife and needle. 
In the first gym screen
Yellow button pieces: On Rope for punching bag and On weight machine (right side)
Move completed yellow button to treadmill.
Get the glowing magazine clue and key piece that appears on the right side of the treadmill.
 
Other pieces in this room:
1. On weight machine, PI star for more time.
2. Bottom of tropy is covering water bottom near green towel.
3. Needle piece on bottom of treadmill
4. On treadmill shaft, trophy and knife handle pieces.
5. key piece on bicycle (near seat).
6. Next to punching bag golden weight piece.
7. Under the table with blender another golden weight piece.
 
Go to Shower area
1. On bench there are three pieces: trophy, tongs, knife.
2. Under sink there is a key piece.
3. Next to trash can there is weight piece.
 
The key should now be complete. Move the key to the locker.
This will unlock the locker to reveal a needle piece and clue (dumbbell)
 
Now that the trophy and needle are completed go back to the main gym room.
Move the trophy to the poster with Jo. Click on the clue.
 
Use the needle to pop the blue exercise ball in the back of the room.
In front of the deflected ball, another clue (protein bar) and piece of the tongs will appear.
Above the weight machine right hand side get the handles for the tongs.
Go back to the shower room. Use the tongs to move the green towel on the lockers.
Get the clue on the locker. A facet piece will appear above the locker.
 
Go back to the main gym room.
Next to the poster of Jo is a piece of the knife.
A piece of the facet is under the boxing gloves.
 
Go to the shower room.
Move the completed facet to the sink.
Click on the phone number that appears on the mirror.
 
Use the knife to cut the shower curtain.
In the shower stall get another clue and final piece of the golden weight.
Put the golden weight on the scale.
Get the last clue.