Zainudin aka Joko Sulistyo, suspected terrorist arrested in Aceh, is the husband of Amrozi's niece living in Jebol hamlet, Boyolali, Central Java.
Amrozi was a convicted terrorist executed in 2008.
Antara news agency reported that Joko married an Amrozi's elder brother daughter in 2009 and took her to live in Jebol.
"Joko's wife has never been registered as a local resident, we did not know her name," Sumiatno, Joko's neighbor, said.
He added Joko's wife, who has a two-month-old baby, had been living with her parent-in-law, Parinem.