The construction worker, a slim man of 18 who had arrived in New York City from Ecuador less than a year ago, returned to his home in Queens one day last month and told his mother about a close call.

A retaining wall designed to hold back soil around the base of a building where he was working had almost fallen, the man, Fernando Vanegaz, had reported. His mother, Enma Ulloa, said it was one in a steady drumbeat of worries he had shared about safety at the construction site in Brooklyn, where a one-story commercial building was being converted into a five-story structure with some residential units.

“He would always tell me about how he had close calls,” Ms. Ulloa said in Spanish on Friday during an interview at the family’s home in Corona, Queens.

The retaining wall fell on Thursday, burying Mr. Vanegaz and two other workers beneath a pile of cinder blocks. The other workers were injured. Mr. Vanegaz was killed.