It’s just after 6 a.m., and traffic is building on Queens Boulevard.

Suddenly, a woman crossing the street at 56th Avenue is struck by a Kia SUV and killed.

The NYPD's Collision Investigation Squad is called; it’s their 331st case this year.

"The collision investigation squad handles all major collisions in New York City, anytime there's a fatality or someone likely to die they go out and do the enhancement and they do the investigation," said Inspector Steve D'Ulisse, the Commanding Officer of the NYPD's Highway District.

The initial evidence: the Kia and the victim's sneakers, still in the road.

"Right now it looks like the vehicle had the green light. The pedestrian tried to cross Queens Boulevard from the north side to the south side against the traffic signal. Pedestrian stepped into the path of the vehicle and then was struck," said Sgt. Robert Denig, of the collision investigation squad.

That account is according to the driver and witnesses, now CIS must check if it's accurate.

"Hi, good morning, I’m Officer Arango with the NYPD’s Collision Investigation Squad. I saw you have some cameras out front?”

Officer Edward Arango begins canvassing for surveillance video with one goal: To understand the crash from the victim's perspective.

"Initially, when I got here, they showed me one set of cameras in the front. Didn't seem to capture it at all. Luckily there was actually a second set of cameras that does seem to capture a portion of the crosswalk in question," Arango said.

At 9:15 a.m., Officer Robert Blinn photographs the scene, including the SUV, and those sneakers, which still have not been moved. His partner, Officer Michael Fitzgibbon, takes measurements to map the site.

"We use our Leica total work station to document the scene properly. To document the lanes of traffic, the path of travel of the motor vehicle. The path of travel of the pedestrian. Any evidence in the roadway," Denig said.

At 10:15 a.m., police tow the SUV for a forensic examination. Fortunately, it has a black box that recorded its speed.

One hurdle: Police don't know the victim's name. But they have one key clue: a pill bottle.

They call the doctor, and learn the woman is 73-year-old Yimei Gao, who lived two blocks away.

Family members are called to the site and driven to Elmhurst Hospital to identify her.

At 11 a.m., the detectives leave for headquarters, to make that map and study the video.

"On this corner here, you can see where the victim is crossing from the north side to the south side. The video captures the whole strike. You can see where the victim lands between the east bound and westbound flows of traffic," said Arango.

"The driver stops pretty quickly exits his vehicle. And you can see signs of shock. He's definitely frantic."

A key clue emerges: The video shows the crosswalk signal. The driver did have the right of way.

"This is where she gets struck, at that point you can actually see the flashing hand for east and westbound pedestrian flow," Arango said.

By 1 p.m., the mystery of what happened is solved.

CIS officers say it's difficult to deal with issues of life and death almost every day, but they find solace in determining exactly what happened and bringing any irresponsible drivers to justice.