Salvatore Perrone, who was held after his initial Brooklyn court appearance on murder charges, denies killing anyone, his lawyer said.
Attorney Ken Jones, who represented Perrone only for the arraignment and hadn't spent that much time with him, said his client shows no remorse and appears "as though he could have some mental-health issues."
Perrone, of Staten Island, will be assigned another lawyer when he returns to court on Tuesday, prosecutors said.
Perrone was taken into custody Wednesday in the suspected serial killings, which scores of detectives were investigating. A pharmacy worker recognized Perrone, 63, as the balding man shown in surveillance footage leaving the scene of the most recent shooting, Nov. 16, with a duffel bag, police said.
Another shopkeeper came forward and said Perrone had gone into his store and questioned him about whether he worked alone and when he closed, police Commissioner Raymond Kelly said.
"It's reasonable to assume he was going to keep doing this, and, by arresting him, we saved lives," Kelly said.
Detectives said they found the duffel bag at Perrone's girlfriend's home. Inside, they said, was a sawed-off rifle used in the killings, along with .22-caliber ammunition, black gloves, women's clothing, a bloody knife and a bottle of bleach.
Perrone's fingerprint was lifted from the murder weapon, Kelly said.
Initially, authorities thought the killer might have targeted the Brooklyn shopkeepers, who were from Iran and Egypt, because of their Middle Eastern backgrounds. But on Wednesday, Kelly said there was no motive he could speak of.
In the most recent killing, Rahmatollah Vahidipour, an Iranian, was shot three times in the head and chest at the She She Boutique.
After that killing, detectives discovered the same gun was used in the fatal shootings of two other shopkeepers when ballistics matched the .22-caliber gun shell casings on all three. On July 6, Mohamed Gebeli, an Egyptian, was found shot at Valentino Fashion Inc. On Aug. 6, Isaac Kadare, also Egyptian, was shot in the head at Amazing 99 Cent Deal.
There were other similarities in the deaths, authorities said: The bodies were all partially obscured, by clothing or, in one case, a box. The locations of the shops form an equilateral triangle and are about 4 miles apart, with addresses that contain the number eight.
Police earlier this week said they were looking to speak to four people who possibly witnessed the most recent killing and released video and clear images of the four. But they zeroed in on the man with the bag, who they now say was Perrone.
Police said they believe Perrone carried the murder weapon in the bag and traveled by subway.
Perrone, a Brooklyn native, is divorced and lives with his girlfriend. He went store to store trying to sell clothing, police said, but it was unclear if he had tried to sell to any of the victims.