The robberies happened on the 2600 block of West Edinger Avenue, and in all four robberies, the suspect threatened the employees with a knife.
The most recent incident happened on Tuesday at 11 p.m. The suspect jumped over the counter, and when employees who were in the back came out, the suspect confronted them, demanding cash from the register.
The first robbery was on June 12 at 6:30 a.m. In that case, he jumped over the counter, grabbed the employee and forced her to show him where the safe was. When she told him she doesn't know where it is, he went to the cash register.
The Subway was robbed again on July 11 and July 17.
The suspect was described as a man in his mid-20s, 5 feet 10 inches to 6 feet 2 inches, 160 to 200 pounds, with a medium build. Police believe he lives nearby.
"He always leaves on foot. Why does he pick this one business? It's open 24 hours a day, but he always goes to this business, he goes when the hours are slow, basically the late night, early morning hours," said Santa Ana Police Cpl. Anthony Bertagna. "He's either watching it, or he's from the neighborhood and he knows the routine."
Anyone with information is urged to call Orange County Crime Stoppers at (855) TIP-OCCS.