The Illinois State Police closed its investigation into the shootings that left five people and the killer dead.
The investigation into the April 24 shooting revealed that Rick Smith planned an attack that witnesses and surviving family members said resulted from a custody dispute over his 3-year-old daughter.
Three families - the Sinclairs, the Luarks and the Ralstons -- lived at the 19 East Street in Manchester at the home that Smith stormed that morning.
None of the victims, including three children at the home, were related to the 43-year-old Smith who lived in rural Morgan County.
Police gunned Smith down later that morning after a chase and a shoot out, investigators said.
JoAnn Sinclair, 66; James Ralston, 29; Brittney Luark, 23; Nolan Ralston, 5 and Brantley Ralston, 1, died in the shooting.
A 6-year-old girl survivor has not been formally identified by police.
A state police statement released Friday said that investigators developed a timeline of Smith's activity prior to the shootings. Cell phone records indicated that he remained within a 25 mile radius of Manchester.
Witnesses told investigators that Smith remained in a custody dispute with a member of the Sinclair family not involved in the shooting.
The Morgan County Sheriff's Department also noted that it facilitated a March 27 exchange of custody between Smith's 3-year-old daughter and her mother, Rita Luark, which occurred without incident.
Investigators said that Smith believed that Rita Luark's relatives were interfering in the custody dispute.