After having made 2.5 million dollars from selling near mint comic books in 2015, Doc set up a bank account under the alias 'Leroy Brown' so that he did not raise suspicion. After all, the real Emmett Brown would have been 95 years old, whereas he was only 65. The plan proved to be successful, as he was able to move around in the future without being labelled a criminal.
The flaw in this plan became obvious on a trip to 2035 to buy parts for the not yet functional Jules Verne Train that he was building in 1893. When Doc tried to withdraw money from the bank, he was detained by the police, as a scan had noticed that his genetic age was not old enough to be the real 'Leroy Brown', as Leroy, 20 years on from 2015, should have been 85, yet Doc was only around 73. With the police officer Griff Tannen in pursuit, Doc escaped the bank and ran back to the steam time car, which he had used to reach 2035 in the first place. Griff tried to use a device that would disable electronic implants on Doc — but since Doc did not have any, it wiped his memory instead. Dazed and confused, Doc managed to return to the date he had seen on Marty's letter — March 3, 1986 — where he ended up crashing into a STOP sign on arrival.