In the days after the massacre, Mr. Basco told KFOX that when he met his wife, “she was an angel, and she still is.”

He said her kindness could not be matched, and that one could see that she was “an awesome lady” simply by looking at how she acted. “We were going to live together and die together,” he said.

Photographs of Mr. Basco kneeling in front of a makeshift memorial of flowers and candles for Ms. Reckard and other victims have been widely shared across social media and by news organizations. Some show him with his head resting against his forearm, his hair spilling out from under a Ford Motor cap, wearing a blue plaid shirt and a wedding band. Others show him kissing a cross with his wife’s name; being consoled by Beto O’Rourke, an El Pasoan and Democratic candidate for president; or wiping tears from the deep lines around his eyes.

Members of Ms. Reckard’s family, including her children who are not related to Mr. Basco, will travel from out of town to be at the service, said Hilda Nuzzi, a daughter-in-law of Ms. Reckard’s.

Ms. Nuzzi never met her mother-in-law but they spoke on the phone and kept up on Facebook. She said Southwest Airlines had offered to fly her and her husband, who is one of Ms. Reckard’s three children, to El Paso, and that other people had offered to pay for lodging.

“It’s overwhelming,” she said. “We really want to thank everybody because they’re not just doing it for my family, they’re doing it for all families.”

Ms. Nuzzi said she lost her sister Tiffani Grissett to gun violence in August 2012 when a man fired into a nightclub in Alabama, killing three people and wounding one. Ms. Nuzzi said she sat through the capital murder trial for the man, who was convicted and sentenced to death row. She said she wanted to do the same for the suspect’s trial in El Paso.