Not having played this game, I can't be of much help here. Have you taken a look at the walkthrough for what you do in Kelsey's apartment? Maybe there is some little thing that you missed:
Click on Boston overview in the map. Drive to Kelsey's apartment.
Look around. Check the posters above the expensive stereo. The 3 posters are that of DJ Ab Horrence, Into the Woods that feature Kelsey and An Evening of Opera that features Kelsey and Colleen.
Read the note left by Kelsey's parents on top of a fancy electronic keyboard at bottom left.
Check the package on the table. It is addressed to Sully. Open it and see a puzzle box.
Puzzle box: Try to open the puzzle box.
Do a synergy action on the box. Click the sphere at bottom left.
Open inventory and select-click the 4 charms that have been collected: bell, piano, guitar and theatre masks.
Click on the synergy icon inside the sphere.
See Kelsey and Joey. Kelsey is upset and opens the 3 monkey puzzle box. She places an SD card inside an envelope.
Another memory: See another memory. Do another synergy action. After using the 4 charms; the 3 parts memory is still fuzzy. More charms are needed.
Open the box: Click the puzzle box now. Erica automatically opens it since the trick was shown by the memory.
Erica sees a vision of Sully and one of his eyes are removed. The box contains Sully's eye, G-clef charm (third victim) and Kelsey's demo CD.
Erica calls her dad for support.
CD: Use Kelsey's demo CD on the stereo. Listen to Kelsey singing.
Check the TV, chair, bed and Erica notes that the furniture are second hand.
Check the mail on the small table left of the bathroom. Take Kelsey's empty envelope.
Check the vent above the small table. It is missing a screw. We need something to open it.
If the above all checks out with what you have done, let's wait and see if a player has any suggestions.
Hope the replay works for you.
That cracked me up. I do the same thing. Glad you're moving on now. Have fun with the game.