Healthy infants just don't die.  The cause of death must be clearly determined and listing "natural" as the cause of death may be appropriate for someone who is elderly but certainly not valid in the case of an infant.  This case is open and a forensic crime scene investigation should take place.  There should also be an attempt to reenact (act out a past event) the event with those that may have been witnesses.  This reenactment should occur at the same time that the event occurred, under the same or nearly the same conditions, and be coordinated with 911 calls and EMS direct testimony.  The reenactment should begin with the time that the child was left at Manu-Lee's home and should list the identities of all parents and children that were at Ms. Lee's home during that day.  The reenactment should include other parents that may have picked up their children after the infant was removed from the scene.  I hope that the detective has photographs of the interior of Ms. Lee's home.