"I will categorically say a body has not been found," Mertz said. "Items that could potentially be evidence have been seized. Nothing that can associated with Annie Le at this time."
Mertz would not confirm reports that the items found included bloody clothing.
Le was last seen Tuesday at a university laboratory. She swiped her identification card to enter the building Tuesday morning, but authorities have found no record of her leaving, despite some 75 surveillance cameras that cover the complex.
Authorities said they still have not determined whether Le's disappearance is a criminal case.
"We don't know where she is. We don't know what happened to her," Yale spokesman Tom Conroy said. "We don't know if a crime was committed or not."
Investigators, having already gone through the videos once, continued to review the surveillance tapes frame-by-frame Saturday to see if they overlooked Le, who could have changed into a laboratory coat or other clothes before leaving the building. Mertz said the review included video enhancement being conducted by state police.
"I do not know if it's definitive if she has left the building at this point," Mertz said. "The last time we saw her on video was entering the building."
On Saturday, investigators took what appeared to be blueprints to the building. FBI agents were also spotted questioning a man outside the lab. When they finished talking, the man got in the front seat of the unmarked car and an FBI agent got in the back seat. The car then drove away.
Yale is offering a $10,000 reward for information leading to Le's whereabouts.
Le, who's of Asian descent, stands 4-foot-11 and weighs 90 pounds. Her purse, cell phone, credit cards and money were found in her office.
Officials say there's no evidence of foul play.
Le, originally from Placerville, Calif., was set to get married Sunday at the North Ritz Club in Syosset, N.Y., on the north shore of Long Island. Workers at the club say the wedding was canceled Friday.
Police say Le's fiance, Jonathan Widawsky, a Columbia University graduate student, is not a suspect and is assisting with the investigation.
At Le's apartment building across town, hopes for Le's safe return waned.
"I feel bad what happened to her," said Anna Beth Funk, who lives across the street from Le's apartment. "It broke my heart hearing she was about to get married because I love being married and it must be so hard for her fiance."
Wesleyan University professor Charles Lemert, who also lives across the street, said Le always took time to talk to his 11-year-old daughter.
"I wish more than anything this could be solved and turn into some kind of misunderstanding, but it seems bleak," he said.