At least twelve of the grand jurors must concur in finding or making an indictment or presentment. They may make a presentment or find an indictment upon the information of two or more of their own body, and when a presentment or indictment is so made, or on the testimony of witnesses called on by the grand jury, or sent to it by the court, the names of the grand jurors giving the information, or of the witnesses, shall be written at the foot of the presentment or indictment.