Passing the results from findObjectsInBackgroundWithBlock into a variable

I'm trying to pass the result from the query into the variable array

var petitions = [PFObject] = []

Then return that result. How I can do that in Swift?

func getPetitions(employeeId: String, employeeBusiness: String) -> [PFObject] {

    var petitions: [PFObject] = []

    var query = PFQuery(className:"Petitions")
    query.selectKeys(["petitionDate", "availableFrom", "availableTo"])
    query.whereKey("employeeId", equalTo:employeeId)
    query.whereKey("employeeBusiness", equalTo:employeeBusiness)
    query.findObjectsInBackgroundWithBlock {
        (objects: [AnyObject]?, error: NSError?) -> Void in
        if error == nil {
            if let objects = objects as? [PFObject] {
                NSLog("Successfully retrieved \(objects.count) petitions.")
                for object in objects {
                    petitions.append(object)
                }
            }
        }
    }

    return petitions
}