The artist, he added, will work with a design committee to finalize plans for the park.
"We're choosing an artist - not a project," Brigham said. The final design, he added, will evolve from a collaborative process that will involve not only the artist, but also other professionals, including a landscape architect, lighting designer and urban planner.
The sculptor will receive an honorarium, plus a budget for creating a centerpiece design, Brigham said.
The Salvation Army already has donated the land for the memorial park and transferred ownership to the city's Parks and Recreation Department.
A committee of private citizens is raising the estimated $450,000 to construct and maintain the park.
The 22d and Market Memorial Park will rise on the site of the former thrift store, which was destroyed on June 5, 2013, during the demolition of an adjacent building.
Four shoppers and two employees were killed when a brick wall collapsed on the store. Among them was Anne Bryan, 24, a PAFA student. The others included Roseline Conteh, Borbor Davis, Kimberly Finnegan, Juanita Harmon and Mary Simpson.
The Pennsylvania Horticultural Society has come up with a preliminary plan for the park, but the project is still a work in progress. After Labor Day, the project will be the subject of a daylong workshop of design professionals.
Harris Steinberg, a member of the memorial park committee and a design professor at the University of Pennsylvania, said the workshop would involve discussion and "fresh thinking" about integrating the memorial garden into the urban streetscape.
The site, he said, is on a corner of Market Street that has the prospect for "considerable redevelopment."
"The garden needs to hold its own on this corner now and in the years to come," Steinberg said. It has to be "both a quiet and contemplative place and an urban design anchor at the busy corner of 22d and Market."
Contributions for the memorial park can be made through PHS at https://www.pennhort.net/memorial.