It is supposed that the robbery was planned many weeks before it took place, and one or more persons familiar with the thorough workings of the bank were suspected of being, to some extent at least, participators in the enterprise. The basement of the premises in question was occupied by a Mr. William Okell, a gentleman well known in the city, and doing business as a broker. Having more room than he required for carrying on his business, he rented out several small offices for business purposes. In the early part of June, a man giving the name of Charles K. Cole, and representing himself as an agent for an insurance company in Chicago, engaged one of these rooms; and to him is given the credit of planning the robbery, in connection with others. Immediately above the office rented to Cole was the president’s private office, and through the ceiling of this office an entrance was made sufficient to admit a man’s body. From the subsequent examination by the detectives, it appears that holes were drilled through this ceiling from above and below, as the Brussels carpet in the president’s room contained no holes, which would not have been the case had the drilling been done entirely from the basement. It was urged by some that this drilling through the ceiling and large beams must have occupied weeks, while other experienced officers asserted that it could have been accomplished in a few hours. One of the severed beams was four inches thick by fourteen in width. Some believed that an entrance was effected through the side door, and that the person or persons had a good knowledge of the employees, where the safes were, the contents of the vault and safes, and the key to the combination lock. [Sidenote: A STARTLING DISCOVERY.] The discovery of the robbery was made by the colored man up stairs, on Monday morning, when he opened the bank, in his usual way, to clean the offices. He detected a strong smell of powder, and went into the rear office to find out the cause of it. There he was astonished at the view which met his Ethiopian eyes. On the floor of this office were the vaults and safes. Here he observed several caps of different descriptions, six or eight in number; overcoats, blouses, and overalls, such as are used by machinists; oil-cloths, rubber shoes, saws, bits, awls, jack-screws, drills, lanterns, and every other kind of implement used by expert thieves. The instruments were gathered together and taken into the possession of the police, and a cabinet of four hundred pieces was made of them. The vault and safes were found to have been broken open; United States bonds were lying scattered about, as well as large quantities of coin and currency, mixed with which were small wedges, railway bonds, copper coin, augers, chisels, flasks of powder, any quantity of cigar stumps, which showed that the burglars took the situation very coolly, pieces of chilled iron, fuses, gold certificates, and other valuable securities.