PITTSBURGH — Two weeks after child welfare workers removed four children from a woman’s suburban Pittsburgh home in June for alleged neglect, they discovered an even bigger problem: The woman has two other children who are missing, and haven’t been seen alive for more than a decade.

Since the summer, police investigators have cast a wide net for twins Ivon and Inisha, who would be about 18 now. A county detective has testified he believes the children are dead but can’t prove it. A cadaver-sniffing dog came up empty during a search of another Pittsburgh area house in December.

Patricia Fowler was arrested in August on charges of concealing the whereabouts of her twins after police investigated following the removal of four of her other children. Fowler has claimed the children are safe and living out of state, but no information she’s provided to police has panned out, authorities said. She’s been free on bail.

As police try to solve the mystery, they have filed additional charges against Fowler, 47, accusing her of illegally collecting more than $50,000 in state food stamps, public assistance and medical benefits for the twins. As of Friday, she had not yet surrendered on the new counts, which include theft.

A criminal complaint filed Wednesday said she had been collecting benefits for the twins since June 2011, and continued doing so through the end of August — weeks after police charged her with concealing the twins’ whereabouts. Her public defender would not comment, citing an office policy to not commenting on pending investigations.