iOS Memory still occupied after removeallobjects and release NSMutableArray

/////////////////////
	//read in test.txt
	NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"test.txt"];
	NSError *error;
	
	NSString *testtest = [[NSString alloc] initWithContentsOfFile:defaultDBPath encoding:NSASCIIStringEncoding error:&error];
	NSMutableArray *Rna = [[NSMutableArray alloc] initWithArray: [testtest componentsSeparatedByString:@"\n"]];
	[testtest release];
	/////////////////////
	//remove all temp arrays
	[Rna removeAllObjects];
	[Rna release];

- (void)applicationDidFinishLaunching:(UIApplication *)application {	
	
	// Override point for customization after app launch	
    MyViewController *aViewController = [[MyViewController alloc] initWithNibName:@"ControllerView" bundle:[NSBundle mainBundle]];
	self.myViewController = aViewController;
	[aViewController release];
	UIView *controllersView = [myViewController view];
	[window addSubview:controllersView];
	[window makeKeyAndVisible];
}
- (void)dealloc {
	[myViewController release];
	[window release];
	[super dealloc];
}

- (IBAction)RnaRns:(id)sender
{
NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"rna.crs"];
	NSError *error;
	NSString *testtest = [[NSString alloc] initWithContentsOfFile:defaultDBPath encoding:NSASCIIStringEncoding error:&error];
	NSArray *Rnaarray = [[testtest componentsSeparatedByString:@"\n"] autorelease];
	[testtest release];
}