Prosecutors say 31-year-old Seth Mazzaglia strangled or suffocated University of New Hampshire sophomore Elizabeth "Lizzi" Marriott in October 2012, after Mazzaglia's girlfriend lured her to their Dover apartment.
Prosecutors say the pair then dumped the Westborough teen's body into the Piscataqua River off Portsmouth's Peirce Island. It has not been found.
Mazzaglia has pleaded not guilty. He told investigators Marriott died accidentally during consensual rough sex.
His former girlfriend, 20-year-old Kathryn McDonough of Portsmouth, is expected to be the key witness against him.
The trial is scheduled to start May 27 and is expected to last at least three weeks.
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