If you haven't done so already, connect the unlocked Android device to the computer directly using the USB cable. The Android device will appear as a new drive and you will be able to access the files on the external storage. If the device is locked, then at this point, you will not be able to access any files and may need to use the Turn on USB storage option, which can be enabled on the phone, as shown in the following screenshot:

With some Android phones (especially with HTC), the device may expose more than one functionality when connected with a USB cable. For instance, as shown in the following screenshot, when an HTC device is connected it presents a menu with four options. The default selection is Charge only. When the Disk drive option is selected, it is mounted as a disk drive:

When the device is mounted as a disk drive, you will be able to access the SD card present on the device. From a forensic point of view, the SD card has significant value as it may contain files that are important to an investigation; however, the core application data stored under /data/data will remain on the device and cannot be accessed with these methods.