He then took a job working as a deputy sheriff in Oldham County, Texas, but was soon fired for picking fights with drunks. He then moved on to Oklahoma, where he worked on several ranches before making his final move to Caldwell, Kansas.

In 1882, he was hired as an assistant marshal in Caldwell and later was promoted to marshal. Brown hired his friend Ben Wheeler, aka: Ben Robertson, to work as a deputy and the two men “cleaned up” the tough town quickly. When Brown felled two outlaws in the streets of Caldwell in 1883, the Caldwell Post bragged that Brown was "one of the quickest men on the trigger in the Southwest." So taken were the town citizens, that they presented him with a new, engraved Winchester rifle.

The marshal continued to serve the city well and the Caldwell Commercial lauded him as "cool, courageous and gentlemanly, and free from vices." In early spring of 1884 he married a local woman, purchased a house and furnishings, and seemingly settled down. However, unbeknownst his wife and the citizens of Caldwell, Brown had been living beyond his means and the debts were mounting.

Falling back on his old outlaw skills, Brown, along with his deputy, Ben Wheeler, and two other former outlaw friends named William Smith and John Wesley, planned to rob the bank in Medicine Lodge, Kansas. The lawmen, under the ruse of traveling to Oklahoma to apprehend a murderer left Caldwell, met up with the two other would-be bank robbers, and headed to Medicine Lodge. On April 30, 1884, they entered the bank just after it opened and demanded the cash. When Bank President E.W. Payne reached for his gun, Brown shot him to death. Though Chief Cashier George Geppert had his hands up, he too was shot. However, before he died he staggered to the vault and managed to close the door.

Their robbery attempt failed, the gang quickly mounted their horses and fled with an angry posse right behind them. Just outside of town the posse trapped them in a box canyon and after a two hour shoot-out, the outlaws finally surrendered. Taken to the Medicine Lodge jail, a mob outside chanted “Hang them! Hang them!”

The outlaws were given a meal, their photo taken, and told to write letters to their families.