var map;
var markers = {};
var bounds = null;
// add marker to object
var posi = new google.maps.LatLng(53.801279, -1.548567);
var name = 'Vince';
markers[name] = {};
markers[name].id = 1;
markers[name].lat = 53.801279;
markers[name].lng = -1.548567;
markers[name].state = 'Online';
markers[name].position = posi;
markers[name].selected = false;

$(document).ready(function() {

  var mapOptions = {
    zoom: 5,
    center: new google.maps.LatLng(53.801279, -1.548567),
    mapTypeId: google.maps.MapTypeId.ROADMAP
  };
  map = new google.maps.Map(document.getElementById('map'), mapOptions);
  var infowindow = new google.maps.InfoWindow();
  for (var key in markers) {
    var marker = new google.maps.Marker({
      position: new google.maps.LatLng(markers[key].lat, markers[key].lng),
      map: map
    });
    markers[key].marker = marker;

    google.maps.event.addListener(marker, 'click', (function(marker, key) {
      return function() {
        infowindow.setContent(key);
        infowindow.open(map, marker);
      }
    })(marker, key));
  }

  // Start drag rectangle to select markers !!!!!!!!!!!!!!!!
  var shiftPressed = false;

  $(window).keydown(function(evt) {
    if (evt.which === 16) { // shift
      shiftPressed = true;
    }
  }).keyup(function(evt) {
    if (evt.which === 16) { // shift
      shiftPressed = false;
    }
  });

  var mouseDownPos, gribBoundingBox = null,
    mouseIsDown = 0;
  var themap = map;

  google.maps.event.addListener(themap, 'mousemove', function(e) {
    if (mouseIsDown && shiftPressed) {
      if (gribBoundingBox !== null) // box exists
      {
        bounds.extend(e.latLng);
        gribBoundingBox.setBounds(bounds); // If this statement is enabled, I lose mouseUp events

      } else // create bounding box
      {
        bounds = new google.maps.LatLngBounds();
        bounds.extend(e.latLng);
        gribBoundingBox = new google.maps.Rectangle({
          map: themap,
          bounds: bounds,
          fillOpacity: 0.15,
          strokeWeight: 0.9,
          clickable: false
        });
      }
    }
  });

  google.maps.event.addListener(themap, 'mousedown', function(e) {
    if (shiftPressed) {

      mouseIsDown = 1;
      mouseDownPos = e.latLng;
      themap.setOptions({
        draggable: false
      });
    }
  });

  google.maps.event.addListener(themap, 'mouseup', function(e) {
    if (mouseIsDown && shiftPressed) {
      mouseIsDown = 0;
      if (gribBoundingBox !== null) // box exists
      {
        var boundsSelectionArea = new google.maps.LatLngBounds(gribBoundingBox.getBounds().getSouthWest(), gribBoundingBox.getBounds().getNorthEast());

        for (var key in markers) { // looping through my Markers Collection 

          //                    if (boundsSelectionArea.contains(markers[key].marker.getPosition())) 
          if (gribBoundingBox.getBounds().contains(markers[key].marker.getPosition())) {
            //if(flashMovie !== null && flashMovie !== undefined) {
            markers[key].marker.setIcon("http://maps.google.com/mapfiles/ms/icons/blue.png")
            document.getElementById('info').innerHTML += "key:" + key + " posn:" + markers[key].marker.getPosition() + " in bnds:" + gribBoundingBox.getBounds() + "<br>";
            // console.log("User selected:" + key + ", id:" + markers[key].id);
            //}   
          } else {
            //if(flashMovie !== null && flashMovie !== undefined) {
            markers[key].marker.setIcon("http://maps.google.com/mapfiles/ms/icons/red.png")
            document.getElementById('info').innerHTML += "key:" + key + " posn:" + markers[key].marker.getPosition() + " out of bnds:" + gribBoundingBox.getBounds() + "<br>";
            // console.log("User NOT selected:" + key + ", id:" + markers[key].id);
            //} 
          }
        }

        gribBoundingBox.setMap(null); // remove the rectangle
      }
      gribBoundingBox = null;

    }

    themap.setOptions({
      draggable: true
    });
    //stopDraw(e);
  });

});

#map {
  height: 500px;
  width: 500px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://maps.googleapis.com/maps/api/js?key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<div id="map"></div>
<div id="info"></div>