Investigators believe a single handgun used in the slayings of two Donaldsonville men in January also was involved in a series of five shooting injuries in recent years in New Orleans.

Ascension Parish Sheriff Jeff Wiley said Friday his officers are in the painstaking process of trying to find and interview the five survivors and witnesses in the New Orleans incidents in an attempt “to find a nexus,” a link between the nonfatal shootings in 2011 and 2013 and the slayings this year in Donaldsonville.

In January, Chad Nichols was fatally shot in the front yard of his home in Donaldsonville. A second man, Benny Booker, who worked in Nichols’ pressure-washing business, was found shot and wounded in the doorway of the home but died at a local hospital shortly afterward.

Early this month, sheriff’s investigators said the double slaying may have been a drug deal that turned into a robbery, after heroin was found in the home.

The Sheriff’s Office learned this month that the same semi-automatic pistol was used in each shooting, although it’s not yet known if the same person fired the gun in each case.

Although the weapon has not yet been found, forensics evidence has been gathered from shell casings found at the shootings, authorities said. A gun’s firing pin strikes the primer on the shell casing to spark the gunpowder and leaves a unique mark on the casing, in this case, evidence of a common link — the handgun — in the wounding of five people in New Orleans and the two Donaldsonville slayings.

The Ascension Sheriff’s Office investigation in New Orleans was hampered, in one respect, by its start a few weeks ago during Mardi Gras season, Wiley said, but has been aided, on the other hand, by the fact that two of the sheriff’s detectives are former New Orleans city police officers and “know the city and the contacts,” Wiley said.

The shootings in New Orleans involving the same semi-automatic pistol are unsolved and the investigations remain open and ongoing, said Frank Robertson, public information officer with the New Orleans Police Department.

Robertson said five people were shot and injured with the pistol in four different incidents, three in summer 2011 and the other in May 2013.

In the first shooting, on July 25, 2011, in the 2300 block of Magnolia Street, a woman was wounded by a gunshot to the back.

Two days later, in the 2500 block of Acacia Street, a 17-year-old boy survived several gunshots to the body.

About two weeks later, on Aug. 13, 2011, in the 1800 block of Conti Street, two men, ages 24 and 25, were each shot in the leg.

Ascension Parish Chief Sheriff’s Deputy Tony Bacala has said that in each of the three 2011 shootings in New Orleans, officers there were told that small groups of people were hanging out together when they were approached and shot at for no reason.

Two years later, on May 2, 2013, the same semi-automatic pistol was fired at a 25-year-old man at the corner of North Dorgenois and Aubrey streets in New Orleans.

According to the NOPD incident report on the case, the man and his friend had left a restaurant about 1:30 p.m. that day, when they were approached from behind by two men, one holding a black handgun.

The victim was told to lie down on the ground, while the suspect who was unarmed went through his pockets, taking cash and his cellphone. The victim got up and ran and was shot in the right arm. The friend with him stood still, and the assailants, one of whom pointed the gun at him, fled, according to the incident report.

The man who was shot was identified as Jessie Bester. He was later arrested after deputies discovered marijuana and crack cocaine in a car he had been driving that day, according to police department documents.

Last month’s slaying of Nichols and Booker in Donaldsonville happened just hours before a rally in downtown Donaldsonville planned in reaction to other shootings in the area.

Advocate staff reporters Jim Mustian and David Mitchell contributed to this story.