Hi just had the scariest moment of my life

noticed a vibration thought it was strange as car had been running fine day before, went to pic dad up from local train station and it got loud so stopped car.
had a look and he noticed back wheel was wobbling

then on closer inspection 3 bolts have dissappeared?
now i know 100% the bolts had been tightened up when i put wheels on so dont know whether someone has tried to steal my wheels then ran out of time/ given up or they had just worked loose.
So question is i have 20mm spacers on rear with these wheels below, what bolts do i need? The bolts came with the spacers so dont even know if they were right ones to start with?
Thanks guys feel a bit shaken up as anything could have happened

(times like this when i feel like someone is watching me up there)
http://www.edition38.com/forums/index.php?showtopic=425911http://www.rimstyle.com/alloywheels/selection/?car_model_id=12930;wheel=cades_bern_hs

Thanks