Derrick Ryan Dearman, 27, turned himself to police in his home state of Mississippi Saturday, hours after he entered the home where his girlfriend was staying with relatives and attacked the people sleeping inside using "firearms and several other weapons," according to a statement from the Mobile County Sheriff's Office.
A 3-month-old baby of one of the victims survived the attack.
"In... a 20-year career as a prosecutor, I have never seen a scene where there were five people brutally and viciously murdered. That's what we have here," Mobile County District Attorney Ashley Rich told CNN affiliate WALA
After the killings, police say Dearman kidnapped his girlfriend -- Laneta Lester -- and the surviving baby.
He drove them across the Mississippi state line to his father's home, where police say Lester and the child were freed. Dearman and his father then went to the Greene County Sheriff's Office in Mississippi where Dearman surrendered Saturday afternoon.
At about the same time, Lester brought the child to police in Citronelle, where she told authorities what had happened.
Police named the victims as Robert Lee Brown, Chelsea Marie Reed, Justin Kaleb Reed, Joseph Adam Turner and Shannon Melissa Randall and Chelsea Marie Reed, who was five months pregnant.
Lester told police she was trying to end what she said was an abusive relationship with Dearman and had gone to stay at the relative's house in Citronelle.
Someone at the residence called police early Saturday morning and reported that Dearman was on the property, but he left before police arrived, a statement from the Mobile County Sheriff's Office said.
Later, Dearman apparently returned to the home and attacked the people inside, the statement said.
Neighbors told CNN affiliate WALA that a brother, a sister and their families lived at the home.
Citronelle is a small community of 4,000 people about 35 miles from Mobile.