By George P. Hassett

A Highland Avenue bank robbed of more than $200,000 in May was again the scene of a heist tonight as a lone masked gunman entered at closing time, tied up four employees, took an undetermined amount of money and fled in a car belonging to one of the employees, according to police.

Police are asking for the public’s help in locating a 2007 gray Infiniti Model G35 coupe with plates reading 21MC99 — the car the suspect is believed to have fled in. They said there is a good possibility it is parked close to the bank.

Police cars raced down Highland Avenue to the East Cambridge Savings Bank shortly before 6 p.m. tonight. More than 10 investigators from the FBI, State Police and local police interviewed bank employees and searched the streets surrounding the bank.

Through a window, bank employees could be seen putting their hands behind their back apparently demonstrating to police how they had been tied up.

The bank was  robbed of more than $200,000, according to a police source, in a May 26 heist that has yet to be solved. In that crime, an employee was kidnapped and held captive for a night prior to the robbery. Police said she was taken to the bank in the morning and, as in tonight’s robbery, was tied up in the basement while the suspect fled in her car.

"It is too early to presume this was connected to anything in the past," said Somerville Police Capt. Paul Upton.

The suspect in tonight’s heist is a 5 foot 10 inch white male, police said. He was wearing a black jacket, dark pants, a knit cap and a mask from his nose to his chin.

As employees were being questioned, Juan Ruiz, 31, looked into the window for his girlfriend who works in the bank. He said the news that she had been a victim in a bank robbery made him question her line of work.

"She ain’t going to work tomorrow," he said.

A mass notification call was sent to every business and residence within a half mile of the bank urging anyone who observed suspicious activity today to contact Somerville police at 617-625-1212.