When Cambridge Police Sgt. Frank Pasquarello was assigned to show the city's new police commissioner, Ronnie Watson, the firehouse on Quincy and Broadway Streets on Wednesday, he never guessed the commissioner would handcuff an alleged purse-snatcher before the afternoon was over.

At 2:24 p.m., Pasquarello and Watson, who has only been commissioner for two weeks, were driving to a meeting at the firehouse when they got a call from the dispatcher about a fight in progress just a few blocks away from them.

Driving to the scene on Divinity Avenue, they found two men wrestling on the ground and swung into action.

"[Watson] jumped out of the car and ran over and helped me handcuff the guy," Pasquarello said.

Edward Sepanek, 44, of 65 Glen Road in Jamaica Plain was arrested by a Harvard police officer and charged with larceny from a building after he allegedly took the purse of a female employee of the Fairchild Biology Laboratory, located at 17 Divinity Ave.

Sepanek was arrested by Officers James Sullivan and Laureen Donahugh, Sgt. Arthur Fitzhugh and Lt. John F. Rooney of the Harvard Police Department.

Sepanek could not be reached for comment.

Sepanek was released after posting bond, according to Peggy McNamara, spokesperson for the Harvard University Police Department, and was arraigned Thursday. No trial date has been set yet.

The man grappling with the alleged purse-snatcher was an employee of the laboratory, according to McNamara. No one was injured, according to Pasquarello.

"It was a great opportunity for the people in the building to help. We didn't have much to do other than assist them," Pasquarello said, adding that he and the commissioner were later teased about their delay in arriving at the firehouse.

"It's a good excuse to be late for meetings," he quipped.

McNamara said Harvard police arrived on the scene after the man had been subdued. After the arrest, the victim emerged from the laboratory building to identify the suspect.

The Harvard Police Department declined to disclose the contents of the purse or the identity of the victim, citing University policy.