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.

The funeral home sits in a strip mall in northeast El Paso and can hold only about 200 people, but up to 1,000 are now expected to attend Friday’s service, including the mayor and other politicians who plan to address mourners. The funeral home is considering moving the service somewhere larger, or having attendees cycle through in groups.

“We’re preparing for it,” said Jorge Ortiz, the funeral home’s general manager. “It’s just about how you organize your personnel and everyone.”

In Mr. Ortiz’s 11 years with the funeral home, this was the first open invitation to a service he could remember. Overflow crowds have been hosted in the past, he said, but never more than about 400 people.

The funeral home’s Facebook post has been shared more than 10,000 times and elicited more than 1,000 comments. One woman wrote that she had sent flowers from Los Angeles. Another man said he would attend the visitation and represent the hundreds of people who could not make it. 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, a daughter-in-law of Ms. Reckard told KTSM.

“We’re going to do everything we can to give her a great send-off and try to give Antonio some closure,” Mr. Johnson said, adding that the funeral home was covering all of the costs.

Mr. Johnson said Mr. Basco had confided in him that he did not really know what to do now that his wife was gone, but that he had been touched by the enormous response to the notice that all were welcome.

Ms. Reckard was born in Washington, according to her obituary, which on Wednesday was receiving tributes from strangers every few seconds.