Best memory management practice for blocks and completion handlers - objective-c

Question

I have the following code in my app, and there is a memory leak with the 'dict' object. So I have a few questions about the best practice for this after the code:
// Convert JSON to dict
NSError *error = nil;
NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
dispatch_async(dispatch_get_main_queue(), ^{
// If error return nil
if (error)
completion(nil, [self handleSerializationError:error]);
else if (![UsefulFunctions objectContainsData:dict[#"data"]])
completion(nil, NO);
// No error then return dict
else
completion(dict, NO);
});
About the code: The completion handler passes back the dict object which is then used to create core data entities (hence the main thread) based upon the calling function. The data being serialised is from an NSURLConnection. So the questions are as follows:
1) Is this the correct practice for passing back data in a completion handler?
2) Which function should take care of the memory management, should it be the calling class?
3) Is it worth wrapping this in an auto-release pool, or is that not how they are supposed to be used (kind of a separate question).
4) Can anyone see any obvious reasons from this function alone why the dict is retained, or is it purely down to the calling class?
Thanks for any help
EDIT (Whole Function), just to confirm I am using ARC and this function is called from the main thread:
- (void)downloadJSONFromURL:(NSURL *)url withCompletionHandler:(void (^)(id object, BOOL retry))completion
{
// Check URL
if (url)
{
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
NSString *authToken = [NSString stringWithFormat:#"token %#", [UsefulFunctions returnActiveAPIKey]];
[request setValue:authToken forHTTPHeaderField:#"Authorization"];
[request setHTTPMethod:#"GET"];
// Create an asynch request, don't want to hold up main queue
[NSURLConnection sendAsynchronousRequest:request queue:[self operationQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError)
{
// If data exists
if (data)
{
// Convert JSON to dict
NSError *error = nil;
NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
dispatch_async(dispatch_get_main_queue(), ^{
// If error return nil
if (error)
completion(nil, [self handleSerializationError:error]);
else if (![UsefulFunctions objectContainsData:dict[#"data"]])
completion(nil, NO);
// No error then return dict
else
completion(dict, NO);
});
}
// If error
else if (connectionError)
{
//NSLog(#"Connection Error: %#, Code: %lu", connectionError.description, (long)connectionError.code);
dispatch_async(dispatch_get_main_queue(), ^{
// Return nil
completion(nil, [self handleConnectionError:connectionError]);
});
}
}];
}
}