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MOORHEAD, Minn. - When a deadly crash happens, family members and the public often want quick answers and justice. This may be especially true when it appears one driver is primarily at fault.

In just the past week, three fatal crashes in Minnesota have people speculating on their causes and asking questions.

Two-year-old Zaiden Engen died after the vehicle he was in was rear-ended on U.S. Highway 10 here on Saturday, Jan. 6.

A Hawley, Minn., woman, 28-year-old Jaynie Halvorson, died when the SUV she was driving collided with a semi south of Hawley early Tuesday, Jan. 9.

Later that day, an East Grand Forks man died in a crash east of Crookston on U.S. Highway 2.

Serious crashes can happen in a split second, so why do they take weeks, even months to investigate?

Minnesota State Patrol Sgt. Jesse Grabow said it's like putting together a puzzle with few instructions. "That's why it's so important for every little piece to come together," he said.

Moorhead Police Capt. Tory Jacobson said while all parts of an investigation are important, some aspects are more complex than others. "Specific science comes into play," he said.

Reconstructing a crash

Once the injured are tended to and traffic is diverted around a crash, officers begin gathering information at the scene.

They'll try to determine whether any driver was having a medical issue or some other impairment. A field sobriety test can be done to check for alcohol or drug use.

The pickup driver, Jeremy Sagvold, 42, of Sabin, Minn., who crashed into the vehicle Zaiden Engen was riding in, showed no sign of physical impairment, police said.

Speed was "definitely a contributing factor" in the crash, Jacobson said, but they are looking at secondary factors, including distraction.

They seized Sagvold's cellphone, a move that's customary after a serious or fatal crash.

Some officers will interview eyewitnesses, and others will photograph vehicles and other evidence. "Stuff from the roadside, tire marks, brake marks, skid marks, those types of things," Grabow said.

In cases of serious injury or death, a crash reconstructionist is called in. The Minnesota State Patrol's west central district has two such experts, who use their technical knowledge to try to determine exactly what happened.

In the days that follow, they calculate weights of vehicles, speeds and many other factors.

Grabow said the most time-consuming aspect of crash reconstruction involves gathering data from a vehicle's onboard computer, also known as the "black box." Officers must first get a search warrant to do so, then download and process the data.

However, all of that information is only part of the story.

"It still doesn't tell you what was going on in the car, doesn't tell you what was going on with the traffic control lights," Jacobson said.

Investigations long, deliberate

The rest of the gaps can be filled in through other means, including surveillance video from nearby businesses and additional interviews.

In the case of the crash that killed Zaiden Engen, Moorhead police asked people who saw what happened to come forward with additional information. Jacobson said investigators received several valuable eyewitness accounts that way.

All of the information gathered is then submitted in a report to a prosecutor - in this case, the Clay County attorney - who will determine whether any charges should be filed and if so, the severity of them.

The process is long and deliberate, for a reason.

"If you're going to charge somebody, you have to be absolutely 100 percent sure," Grabow said.

Jacobson recognizes that people will always speculate when it comes to serious crashes, but he's careful not to release too much information, too soon.

"Among the community that is looking and reading and listening to what's being said about this event is the people that are involved in it. It's very tragic for all of them, it's very difficult, and it needs to be handled sensitively," Jacobson said.