With the sci-fi element, maybe make "Jack" an original character-- 21st scientist or doctor who fled to the past and is killing victims to isolate something that could be tied to the global catastrophe that threatens the present.
Jack the Ripper is an enigma. He's bigger than the Whitchapel crimes, really. He's become a legendary symbol of pure evil... And also used to sell books and t-shirts. We don't know who he is, and are perhaps reluctant to admit he might have just been one of us.
: Jack the Ripper plays shuffleboard. -- Happy Birthday, Wanda June
by Kurt Vonnegut, c.1970.