search and filter gridview based on Querystring value in ASP.Net

I got the value from the previous page but i am not able to query the databsase to get rows with string id

string id = Request.QueryString["custid"];
DataTable da = new DataTable();
using (SqlConnection conn = new SqlConnection(strConnString))
{
    string strQuery = "SELECT * FROM LoanMaster where custId=@custId";
    SqlCommand cmd = new SqlCommand(strQuery);
    SqlCommand insert = new SqlCommand(strQuery, con);
    insert.Parameters.AddWithValue("@custId", id);
    using (SqlDataAdapter sda = new SqlDataAdapter())
    {
        cmd.Connection = con;
        conn.Open();
        sda.SelectCommand = cmd;
        sda.Fill(da);
        GridView2.DataSource = da;
        GridView2.DataBind();
    }
}