The so called "ninja robber" tries hitting a North Miami Beach convenience store for the third time.

Late Tuesday, surveillance cameras caught the robber trying to get inside the Kwik Stop at 18198 Northeast 19th Avenue. He had already robbed the store twice.

However, the robber was unable to get inside the store because it was locked. Police said only the clerk inside the store could open the front door by using a switch.

"He tried to open that door. The door was locked," said M.D. Islam, the clerk, who acted a silent alarm when he saw the robber.

The robber ran off. Two minutes later, a customer walked in, and three minutes later, police arrived.

The FBI is offering a $5,000 reward for information leading to his arrest. Police said he has robbed at least a dozen businesses in the last three months, including:

• Date/Time: May 12, 2012 at 11:04 pm
  Location: Kwik Stop, 17200 West Dixie Highway
• Date/Time: June 23, 2012 at 10:55 pm
  Location: Shell Gas Station, 1420 East Sunrise Blvd
• Date/Time: July 1, 2012 at 10:41 pm
  Location: Petrolio Gas Station, 1554 South Federal Highway
• Date/Time: July 13, 2012 at 12:18 am
  Location: Kwik Stop, 18198 NE 19th Avenue
• Date/Time: July 15, 2012 at 9:45 pm
  Location: Chevron Gas Station, 13005 Biscayne Blvd
• Date/Time: August 3, 2012 at 9:40 pm
  Location: Marina Discount Beverage, 2705 SW 15th Avenue
• Date/Time: August 6, 2012 at 1:05 am
  Location: Chevron Gas Station, 4051 Stirling Road
• Date/Time: August 14, 2012 at 4:26 pm
  Location: Citgo Gas Station, 15200 Biscayne Blvd
• Date/Time: August 15, 2012 at 7:00 am
  Location: Badoma Plaza, 1989 NE 19th Avenue
• Date/Time: August 18, 2012 at 11:59 pm
  Location: Kwik Stop, 18198 NE 19 Avenue
• Date/Time: August 22, 2012 at 12:58 am
  Location: Citgo Gas Station, 2109 Griffin Road

North Miami Beach police said he has robbed six stores in their city alone.

"What concerns us, the numbers are increasing," said North Miami Beach Police Chief Thomas Carney. "If the store clerk resists or an innocent customer walks in on it, then the chances of getting hurt is pretty high."

In some of the robberies, the man was out of the store in a few seconds. In nearly all of them, he's seen terrorizing the clerks, including holding a gun to one man's head as he took money out of the cash register.

"Two of my people they already told me they don't want to work," said Sanjoy Saha, the manager at the Kwik Stop at 18198 Northeast 19th Avenue.

In one robbery, one clerk fought back, but the robber managed to get away.

In another video, the robber put a gun to a female customer's head.

"He entered the store and immediately went to a customer and put a gun to her head and ordered the cashier to give him the money or that he would kill her," said North Miami Beach Police Detective Mike Stein.

The robber typically wears a black hoodie and a mask that only reveals his eyes. He always wears blue or purple latex gloves and black sneakers with a white sole.

The FBI, Broward Sheriff’s Office, North Miami Beach PD, Fort Lauderdale PD, North Miami PD and the South Florida Violent Crime Task Force are all investigating.

Anyone with information on the identity of the robber is asked to call the FBI at 305-944-9101.