I bought a ipad mini, but now cant contact previous owner to get his apple id and password to start the ipad.

SOURCE: ipad ver 4.ios7, how can I remove previous owner from ipad? ive removed pasword and I cannot contact last owner

Go into setting and then "Reset". Then choose to reset all and delete all content from previous owner.

SOURCE: how to set up password on my new ipad mini

The following can be done on ipad with iOS 8:
1. Press the home button( the round button on the front side of your ipad), to go to the home screen.
2. Find the Settings icon ( looks like gray clockwork gears) and tap on it to launch the Settings app.
3. After settings app is started try to find on the left side of the screen Passcode ( has a red lock icon near the text) and tap on it
4. In the passcode setting screen you can choose the type of passcode with the Simple passcode setting switched on or off ( simple means a 4 digit number, not simple means any character combination
5. By taping on Turn passcode on you can enter your passcode. Be carefull not to forget your passcode, otherwise you will not be able to use your ipad later.

SOURCE: I have two Apple ID's on my iPad. How do I get rid of one if I don know the password or security questions?

Your best source of help would be to call Apple. They go out of the way to support there products.

SOURCE: how do i factory reset apple ipad i forgot my apple id and password

Resetting the ipad will not help... The I'd and password are stored at the apple store.