A spokesman for Iowa Attorney General Tom Miller will not predict how much longer it will take to reach a settlement with the nation’s five largest mortgage banks. Miller is leading a 50-state investigation into improper foreclosure practices.

Geoff Greenwood, a spokesman for Iowa’s attorney general says, “We began this effort back in mid-October and we’ve been working on this case every single day. “It’s a very complicated case. There are a lot of moving parts and there are a lot of people involved.”

 The attorneys general launched the investigation after reports that big banks used flawed documents to foreclose on hundreds of homes.

“This is something that we think is very important and we’re working very hard at trying to reach a satisfactory settlement,” Greenwood says. A settlement could require the banks to pay penalties or to rewrite some troubled home loans. Greenwood says one unresolved issue is whether banks that sign on to a 50-state settlement should be immune from state and federal prosecution for their mortgage practices.

Miller and the rest of the country’s attorneys general are in talks with Bank of America, Citigroup, JPMorgan Chase, Wells Fargo, and GMAC. Those companies hold nearly 60% of all U.S. home mortgages.