SHEIKHUPURA - The City B Division Police have registered a case against unknown car-riders who attempted to throw heroin through tennis ball into district jail the other day.  According to details, two unknown car-riders parked the car by the wall of district jail and attempted to throw the ball filled with contraband weighing 30 gram into the jail. In the meantime the jail staffers spotted the culprits and informed the City B Division Police. On seeing the police, the car-riders made good their escape.  It is to be noted recently the criminals have made hectic efforts to smuggle contraband to but due to strict security measures failed to succeed.