Orange County sheriff's officials took the suspect into custody on Friday. No further details were immediately released regarding the identity of the suspect.
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Sheriff's officials were expected to hold a press conference at 4 p.m. to discuss the case.
Bernstein's body was found Tuesday in the brush along the perimeter of Lake Forest's Borrego Park after he had been missing for a week. Investigators said they are treating his death as a homicide.
MORE: Search warrant provides new details into investigation of OC student's death
New details emerge on OC student's death
The University of Pennsylvania student was last seen entering Borrego Park at about 11 p.m. on Jan. 2 by a friend who was with him at the time.
A search warrant, which has since been sealed, recently revealed details of the investigation.
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An affidavit described detectives' interview with that friend who drove Berstein to the park the last time he was seen alive.
The friend said he and Bernstein spoke on Snapchat that night of Jan. 2 and made plans for the friend to pick him up. The friend said he seemed depressed, but didn't say he wanted to hurt himself.
They drove to the park. The friend said Bernstein then walked alone into the darkness.
Bernstein didn't respond to messages, so the friend said he left and went to a girlfriend's house, then returned to the park later.
Bernstein was reported missing the next day. His parents said he left the house with no wallet, money, identification, keys or eyeglasses.
Detectives say as they were interviewing the friend, they noticed scratches and abrasions on the friend's hand. He said it was from a fight club.
They also saw dirt under his nails. He said it was from falling into a puddle.
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They also said during the interview he appeared nervous, was talking fast and was visibly shaking. At one point, he pulled his jacket over his hands to prevent his fingers from touching doors.
The detectives interviewed the friend more than once and say his story remained consistent.
As the investigation continues, friends in Orange County, and at the University of Pennsylvania where he attended, have been mourning Bernstein.
A candlelight vigil was held Wednesday at Borrego Park in which friends mourned the loss and expressed support and prayers for his family.