WEYMOUTH — Around 1:20 a.m. on a Sunday last August, Weymouth officer Edward Hancock spotted a speeding white Ford Explorer. After a chase into Quincy, a crash, and a struggle on foot, Hancock arrested the driver, Ryan Bois. In the SUV’s back seat, Hancock found 6-year-old Joanna Mullins, dead.

The following day, Bois was charged with murder in the killing of Mullins, his young cousin.

On Monday, Hancock will be recognized for his efforts that summer night. He will be the only law enforcement officer in Massachusetts honored by the National Association of Police Organizations, the group that issues the annual “Top Cop” award.

Last Aug. 5, Bois hit speeds of up to 100 mph before slamming into a cab. After the crash, he attempted to flee, pulling a knife before being arrested by Hancock, with the help of his police dog, Hax.

Hancock, a 10-year veteran of the force, said the experience touched on the range of emotions a police officer feels on the job.

“I’m getting an adrenaline rush getting into a car chase and a full pursuit,” Hancock said. “Then you’re excited that you did your job and you caught somebody fleeing from you.

“Then it went to the lowest point of seeing a young, lifeless child in the backseat of a car It was almost shock and awe.”

Hancock will travel to Washington, D.C., on Monday to receive an honorable mention award. The event will be emceed by “America’s Most Wanted” host John Walsh.