The third Southwest City bank holdup occurred on February 16, 1955, when three men entered the bank about eleven o'clock in the morning armed with .45 caliber revolvers. One bandit approached assistant cashier James Cantrell's window while the other two robbers herded four other employees and three customers to the rear of the bank and made them lie down. Cantrell was ordered to open the vault, but he claimed he couldn't because it was a time lock. Cantrell was then taken to the rear of the room and exchanged for a second assistant cashier, who opened the lock after the gang threatened to shoot him. The bandits, none of whom wore masks, made off with about $50,000. They were driving a 1953 or 1954 black four-door sedan and headed north toward Joplin.
On February 18, just two days after the holdup, the FBI announced the arrest of two men in connection with the robbery. Glen Howard Potter, 53, was arrested on the night of the 17th on his farm near Southwest City, and Jack Cope, 29, was taken into custody on his farm near Delmar, Arkansas, on the morning of the 18th. Over $12,000 in loot was recovered at the time of Cope's arrest, and over $3,000 was found at the Potter place. Cope was charged as an actual participant in the robbery, and Potter was charged with knowingly receiving stolen property. Also named as suspects in the robbery but not yet arrested were Potter's brother, William Budshaw Potter, 49; a man tentatively identified as Frank Haley; and Glen Potter's daughter-in-law, Margaret Potter, 23. She had allegedly received about $1,300 of the loot. Glen Potter was from Chicago, but he had recently purchased the McDonald County farm. William Potter and Haley were still at large and were considered armed and dangerous.
The next day, February 19, it was announced that both fugitives had been taken into custody, and that $45,000 of the stolen money had now been recovered. About $12,500 was found hidden under a house in Wheatfield, Indiana, where Ray Louis Curtis, 28, (alias Frank Haley) was arrested. William Potter of Thayer, Missouri, was arrested near the same time as Curtis, and another $13,000 was found on his farm. Margaret Potter was arrested about the same time as William Potter and Curtis, after Glen Potter admitted giving some of the loot to her.
All five defendants went to trial in Kansas City in June 1955, and all five pleaded guilty to an assortment of charges. As the three principals in the robbery, William Potter was sentenced to 32 years in prison, Cope was sentenced to 32 years, and Curtis was sentenced to 12 1/2 years. Glen Potter got two years for receiving stolen property, while young Mrs. Potter's sentencing was deferred. Later the same year, she received a suspended three-year term and was placed on probation.