The answer to this question is a ***SPOILER*** It wasn't Eli or Hugo. You will find that out a few cases later in the Quarter Moon Murders. For a guide to the Golden Butterfly, follow this guide: http://www.sleeandtopher.com/guide/l-a-noire-the-golden-butterfly-case-guide/
For a guide to the Quarter Moon Murders, follow this guide: http://www.sleeandtopher.com/guide/l-a-noire-the-quarter-moon-murders-case-guide/