A "middle-aged man" whose safe deposit box contained $8,000 was the object of a large-scale search by police last-night in connection with the January 9 robbery of the Coop.

Police declined to identify the man further until a definite link with the $50,000 Coop theft had been established.

This latest step in the police drive to apprehend the four men who pulled the smoke bomb stickup followed hard on the heels of Tuesday's arraignment of Nicholas Mavrides, 39, of 38 Prince Street, Cambridge, on charge of having participated in the holdup.

Mavrides Hold

Mavrides was held in 360,000 double surety bond by the Middlesex County Superior Court. Trial of the case was postponed indefinitely in the hope that his alleged partners could be arrested and tried at the same time.

Yesterday's development came when police sought to examine the unidentified man's safe deposit box in a Newton bank. Armed with a search warrant, a squad, made up of Cambridge, Newton, and State police, drilled open the box when its owner claimed that he had lost the key.

Box Owner Vanishes

It took two hours to count the $8,000 in the presence of bank officials, and when this process was over, the police squad found that the suspect had disappeared.

At the same time, another lead was being tracked down by Cambridge sleuths as they traced the materials used in making the two smoke bombs employed to confuse Coop customers.