Othniel Miller, 75, was a handyman who worked in a basement near the building where Etan lived with his parents. Investigators began searching there this week after a cadaver dog picked up signs of human remains.
"Mr. Miller has been cooperating with this investigation for over 30 years," lawyer Michael Farkas told CNN. "He has continued to cooperate on multiple occasions. And I am going to assist him in cooperating to the fullest extent possible."
The search is to include digging up a concrete floor that had been recently poured when the hunt for Etan began.
Etan vanished May 25, 1979, during a short walk between his home in the SoHo neighborhood and the school bus stop. At the time, SoHo, now a trendy high-income neighborhood, was home to artists who moved into lofts that had usually been used for light manufacturing.
Stan and Julie Patz still live in the same building. They posted a sign outside telling "the hardworking and patient media people" they have no comment.
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