Mazzaglia Ex-Girlfriend: I Told Grand Jury About UNH Murder Without Plea Deal

DOVER, N.H. (AP) – The ex-girlfriend of the man prosecutors say raped and killed a 19-year-old University of New Hampshire student says she had no plea deal in place when she told a grand jury what happened the night Elizabeth "Lizzi" Marriott died.

Nineteen-year-old Kathryn McDonough says she had been granted immunity, but did not know what sentence she would receive on pending charges of hindering prosecution and conspiracy. She testified before the grand jury and at trial that 31-year-old Seth Mazzaglia killed Marriott after she rebuffed his sexual advances Oct. 9, 2012.

Lawyers on both sides agree jurors' perception of McDonough's credibility is critical key to Mazzaglia's fate.

Mazzaglia was arrested four days after Marriott was killed. McDonough says she and Mazzaglia dumped her body into a river. It has not been found.

Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

MORE LOCAL NEWS FROM CBS BOSTON