CBS News Correspondent Randall Pinkston spoke to a medical student who, like Le, worked alongside Clark. She requested that CBS News obscure her face and voice.
Friday night, three days after Le vanished, and before her body was found, the woman says she was in the basement, about five feet from him for roughly three minutes.
"He appeared very relaxed, very normal," the woman told Pinkston. "I didn't sense any anything different in his behavior from what I'd observed previously."
Only essential personnel could access the basement lab, by swiping key cards at multiple access points, Pinkston points out. The area was highly secured. And researchers typically worked alone.
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The med student observed to Pinkston that it is "so secluded down there, soundproof, and nobody is ever looking for you, nobody questions when you go into a room for several hours and don't come out."
The "perfect place," Pinkston noted, for a murder.
A high school friend and baseball teammate of Clark's told "Early Show" co-anchor Harry Smith Thursday he found it "shocking" when Clark was named a person of interest in Le's killing, days before Thursday's arrest announcement.
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"I remember Ray as a friendly guy, a personable guy," said Conor Reardon, who attended Branford (Conn..) High School with Clark and graduated in 2004, "certainly toward people that he knew well. I know that he had a tendency to be a little bit shy, perhaps, around people that he didn't know. And so, if someone had described him as withdrawn or aloof, they wouldn't necessarily have been way off the mark, but once you got to know him a little bit, he was friendly, he was respectful, he was personable. I actually liked him quite a bit. He was a good guy."
And when he heard police were looking at Clark, "It was shocking, certainly. Really shocking, you know. I would have been shocked to hear that anybody that I knew was a person of interest in the case."