Thief Caught in The Act

I came home last night about 11:15 to find a thief in my doorway, zipping up a backpack. I started yelling at the top of my lungs, threw my skateboard down, and ran at him. He was startled, dropped the backpack, and began running down the beach. I chased him a little bit, but I was worried there might be others in the house. I came back and no one else was here, and I couldn't see anything missing. I found the backpack on the beach--it was my roommates. Later when my roommates came home, two of them discovered their wallets were gone. I'm also missing my shampoo. If I had come home five minutes later, he probably would have taken everything--computers, cameras, guitars, etc.