I'm still on the fence, but here's a scenario with Lauren at JR's apt at 3:10, and at Tenth & College with mystery man at 3:38.
Lauren and CR walk from Smallwood to CR/MB's apt. MB puts CR to bed (3:10?), Lauren goes to JR's to party some more. JR falls asleep; Lauren leaves around 3:30 and is spotted at 3:38 by the witness at Tenth & College. Later that day JR hears that Lauren is missing; he lies about watching her leave at 4:30...she was fine...not stumbling...so he doesn't look like such an awful person for not walking her home.
JR's visiting friend could have been asleep in one of the bedrooms, or too drunk to care that Lauren was leaving without shoes, keys or cell phone. Hard to explain the 4:15 call to DR. Maybe JR woke up, noticed she was gone, and called DR to see if she was back at Smallwood.
And there might not be any video of 3:38 sighting if it happened on the sidewalk on College- outside of the breezeway.
JMHO