We watched as crime scene investigators removed sections of carpet from the store, while others re-interviewed the store's owners.
Technicians went door-to-door on Madison Avenue seizing video from area surveillance cameras.
A source familiar with the investigation said there is no video from inside the store because the security system failed to record the robbery. On Thursday night, NYPD released video of a person of interest captured in the vicinity of the store on Wednesday at about the time of the incident. (CLICK HERE TO SEE THE VIDEO)
Investigators say the store's remote-controlled door was also out-of-commission. That allowed an otherwise suspicious-looking man to walk right in with a loaded handgun.
Two people were working at R.S. Durant at about 12:25 p.m. on Wednesday when the bandit walked inside.
The workers refused to fill two canvas bags the gunman brought, police said. The suspect took out the clip from his semiautomatic pistol and showed it to the employees, saying, "You think I'm kidding? This is real" before putting the clip back in and firing once, said NYPD spokesman Paul J. Browne.
Henry Menahem, 71, was hit once in the chest. The second worker, a 49-year-old man, asked if he could call 911 to help Menahem, but the gunman refused.
The gunman smashed one of the cases and loaded bags with diamond necklaces and other jewels before fleeing south on Madison Avenue. No customers were in the store, located between 75th and 76th streets, at the time.
Authorities said he made off with 66 items valued at more than $1.2 million.
The suspect is described as a light-skinned, African-American man, 5'10", 160 pounds, wearing a blue wool coat, gray trousers, black dress shoes and a scarf. The suspect also wore sunglasses and black gloves -- an indication, police say that he may have been a professional thief.
He clearly knew enough to walk calmly out onto Madison Avenue, past hundreds of afternoon shoppers with a bag full of gold and diamonds after killing the clerk in cold blood.
NYPD has released photos and a list of the jewelry stolen during the robbery.
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Anyone with information is asked to call the NYPD's Crime Stoppers Hotline at 800-577-TIPS.