MY GIRLFRIEND GOTkidnapped BYMEN IN MY APARTMENT

My girlfriend and I live in a high-rise apartment (a tower that's 26 stories tall). When we first moved in they told us that only homeowners/renters can access the stairs behind the front doors (with or without a keycard). So, one day when we were getting groceries, the elevator broke and we had to climb the stairs to get in. When we got back home, the front door was wide open. I thought nothing of it and went to sit on the couch to wait for my gf to open the door. I noticed that our computer was missing and they had gone into our desk. I was extremely confused and asked my gf how the thieves got in but she said she didn't know. I went to the kitchen to see if they had stolen anything else and the balcony front door was open. So I went outside and noticed that a piece of the railing was missing/broken and that the window was open. I was extremely worried because I didn't see my gf until I came back in the house and she was sitting on the couch. I asked her what happened and she told me that they came behind her in the hallway, took her and brought her in through the balcony window behind mine after they broke the railing. I was extremely confused because the only way to access the stairs behind the front door is with a key card. I asked the front desk how they got in and they said they came in behind my gf after she opened the door in front of the building and nobody stopped them. I was stressed to say the least. I could not sleep for a week and I got a few cameras and an alarm installed in the house as well as a motion sensitive flashlight in the balcony. I can't believe what happened. I can't believe how they got in and how they left. We have filed a police report and I contacted the owner of the building and told them what happened. We are planning on moving in the next few months but the craziest part is that they didn't steal anything but the computer. I guess they might have been looking for something in the desk because it was open. Please let me know what you think might have happened. Thank you