The first robbery happened around 2:24 p.m. on June 13 at the PNC Bank along E. Dekalb Pike.
Police say the victim was walking away from the ATM when the suspect produced a knife and demanded money.
Then on June 14, the same suspect approached another victim around 1:25 p.m. near the AAA- Mid Atlantic building on East Dekalb Pike.
Police say the suspect demanded a woman's purse while at knifepoint.
Officers were able to arrest 51-year-old Jonathan Hemberger, of Phoenix, shortly after the second incident.
Surveillance video linked Hemberger to both robberies.
He's facing multiple charges and is now being held on $500,000 bail.
No one was hurt during the robberies.