uses
  System.JSON;

const
  cJson: string =
    '{"response":{"count":204,"items":[{"id":154770,"body":"","user_id":1,'+
    '"from_id":1,"date":1492002564,"read_state":1,"out":0,"random_id":965793707,'+
    '"fwd_messages":[{"user_id":1,"date":1492002563,"body":"","fwd_messages":'+
    '[{"user_id":1,"date":1492002561,"body":"кек","fwd_messages":[{"user_id":1,'+
    '"date":1492002534,"body":"лол","fwd_messages":[{"user_id":1,"date":'+
    '1492002530,"body":"","fwd_messages":[{"user_id":1,"date":1492002528,'+
    '"body":"","fwd_messages":[{"user_id":1,"date":1492002512,"body":"",'+
    '"fwd_messages":[{"user_id":1,"date":1492002510,"body":"","fwd_messages":'+
    '[{"user_id":1,"date":1492002508,"body":"","fwd_messages":[{"user_id":1,'+
    '"date":1492002506,"body":"","fwd_messages":[{"user_id":1,"date":1492002504,'+
    '"body":"","fwd_messages":[{"user_id":1,"date":1492002499,"body":"",'+
    '"fwd_messages":[{"user_id":1,"date":1492002497,"body":"","fwd_messages"'+
    ':[{"user_id":1,"date":1492002494,"body":"","fwd_messages":[{"user_id":1,'+
    '"date":1492002492,"body":"","fwd_messages":[{"user_id":1,"date":1492002490,'+
    '"body":"","fwd_messages":[{"user_id":1,"date":1492002488,"body":"",'+
    '"fwd_messages":[{"user_id":1,"date":1492002486,"body":"","fwd_messages":'+
    '[{"user_id":1,"date":1491925392,"body":"","fwd_messages":[{"user_id":1,'+
    '"date":1490901947,"body":"test message"}]}]}]}]}]}]}]}]}]}]}]}]}]}]}]}]}]}]}]}],'+
    '"in_read":155942,"out_read":155942}}';

procedure DoTest;
var
  VStr: string;
  VJsonValue: TJSONValue;
  VJsonObject: TJSONObject;
begin
  VJsonObject := TJSONObject.ParseJSONValue(cJson) as TJSONObject;
  if VJsonObject <> nil then begin
    try
      if VJsonObject.TryGetValue('response["items"]', VJsonValue) then begin
        VStr := VJsonValue.ToJSON;
      end;
    finally
      VJsonObject.Free;
    end;
  end else begin
    // handle json parser error
  end;
end;