How to add alphabetic sections in TableView from database using swift 3 - ios

Question

I'v created a TableView that shows data from my database, now I want to add alphabetic sections into my table my database already sorted alphabetically.
My problems:
1 - I can't make the Dictionary to accesses only the first column of the database (the name column).
2 - I don't know how to get the first letter of the names and store every item in the letter the name start with.
If you know a better way than using a Dictionary I'm open to any suggestions.
My code:
class crimesTableViewController: UITableViewController {
var marrCrimesData : NSMutableArray!
#IBOutlet weak var crimesTableView: UITableView!
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(_ animated: Bool) {
self.getCrimesData()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
func getCrimesData()
{
marrCrimesData = NSMutableArray()
marrCrimesData = ModelManager.getInstance().getAllCrimesData()
crimesTableView.reloadData()
}
// MARK: - Table view data source
override func numberOfSections(in tableView: UITableView) -> Int {
// #warning Incomplete implementation, return the number of sections
return 1
}
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
// #warning Incomplete implementation, return the number of rows
return marrCrimesData.count
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell: crimesTableViewCell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! crimesTableViewCell
let crime: CrimesInfo = marrCrimesData.object(at: indexPath.row) as! CrimesInfo
cell.nameLabel.text = crime.Name
cell.detailLabel.text = crime.Detail
cell.timeLabel.text = crime.Time
return cell
}