Peterson, a retired Bolingbrook, Ill., police sergeant, is charged with murder in the death of his third wife, Kathleen Savio. Police have said he's also a suspect in the disappearance of his 23-year-old fourth wife, Stacy Peterson, who vanished in October 2007.
Stacy Peterson allegedly told a minister that her husband killed Savio, prosecutors have said.
Under the new law, known as Drew's law, that statement and others allegedly made by Savio could be admitted as evidence in the murder case against Peterson, whose lawyers Monday asked Will County Judge Stephen White to find the law unconstitutional.
The U.S. Constitution guarantees Peterson the right to confront an accuser in court, something he cannot do in this case, lead defense lawyer Joel Brodsky said.
Similar hearsay laws are in use in 12 other states, the Joliet (Ill.) Herald-News reported Tuesday.