Deciding which police officers killed in the line of duty belong on a national memorial usually is driven by facts and presents few obstacles. But this year, two cases show that it isn’t always so black-and-white to honor the nation’s fallen men and women in blue.

This year, the cases of two inductees highlight different challenges facing leaders of the National Law Enforcement Officers Memorial Fund, which holds a vigil today for 321 officers added to the wall in Washington, D.C.

Detective Sgt. Caleb Embree Smith of the Flint (Mich.) Police Department died by poisoning in 1921, and Wauwatosa, Wis., Officer Jennifer Sebena was shot multiple times while working last Christmas Eve. Her husband has been charged in her death.

The final decision by the memorial board last month to include Sebena was ultimately unanimous but came after pressure from lawmakers, police and Wisconsin Gov. Scott Walker.

The group’s board reversed its original rejection of Sebena’s bid that was based on the belief that she died as a victim of domestic violence. But after reviewing hundreds of pages of reports, and speaking with the local police chief and prosecutor, the board decided Sebena died in the line of duty and deserved to be honored.

Smith’s nomination also received unanimous approval and didn’t require a reversal, but the nearly century-old case came with its own shades of gray: He was poisoned, though it was never determined how or by whom. Despite the passing of time, missing pieces and unusual cause of death, the group determined it was a line-of-duty death.

“It would be easy to say OK to everyone,” said Craig Floyd, the fund’s chairman and chief executive. “We do need to give that wall a certain integrity.”

The integrity, Floyd said, comes through following a process and abiding by certain rules, even if it means facing scrutiny, such as with the Sebena case. The nonprofit organization requires that in order to be chosen for inclusion on the wall, the officer must have died in the course of duty and served directly for a governmental agency with the powers to arrest.

He said the group first saw the Sebena case as a “death of personal nature” and not one because of her work, and said similar cases previously had been denied. But officials with the Wisconsin Professional Police Association found other officers honored by the group had died in similar circumstances.

Floyd said a closer look provided clarity: Authorities accuse Benjamin Sebena of ambushing his wife from behind as she conducted a routine solo patrol in the Milwaukee suburb. The Iraq War veteran pleaded not guilty by reason of insanity to the charge of first-degree intentional homicide, and his trial is scheduled to start in July.

“She was clearly murdered while on duty — in uniform,” Floyd said. “Upon reconsideration, we came to a different conclusion — I think the proper conclusion.”

Some cases lack controversy but require scrutiny because of their age and various peculiarities. Such was the case with the Flint officer Smith, who died within hours of eating his lunch Oct. 27, 1921. The cause of death was arsenic poisoning and an autopsy found trace amounts of strychnine and other chemicals in his body.

Floyd said Smith’s case, researched by his granddaughter, Kathleen Smith, and Flint police Sgt. Greg Hosmer, was unusual for investigators because it involved poisoning and it was never solved. He credited the careful investigation by family and police as well as the department’s recommendation.

“We didn’t believe we met the criteria in D.C. to have him honored, but we did the best we could to at least have him memorialized here in this city,” said Hosmer, a veteran investigator of the city’s cold cases. “As far as I was concerned, he died in the line of duty. We did send it on to D.C., in hopes that they would see it differently.”