Wichita ? Investigators have tracked down a missing communication that may have come from the BTK serial killer, leading police to again appeal to the public for help in solving the case.

Wichita television station KAKE received a postcard Tuesday that led police to a suspicious package in a rural area northwest of Wichita. That postcard also inquired about an earlier undiscovered communication, which police said they found Wednesday night.

Police believe the package could be connected to BTK and have submitted its contents to the Federal Bureau of Investigation, police Lt. Ken Landwehr said Thursday. He did not elaborate on its contents and refused to take questions from reporters.

BTK — which stands for “Bind, Torture, Kill” — has been linked to eight unsolved killings from 1974 through 1986. He resurfaced in March with letters to media and police.

The package referenced in the postcard — which the sender called communication number eight — was found on North Seneca Street, a dirt road that runs between 69th and 77th streets in a rural area northwest of Wichita. Landwehr said police wanted to talk to anyone who may have seen any suspicious activity in the area between Jan. 14 and 25.

KAKE aired footage of the package, a Post Toasties cereal box, weighted down with a brick, leaning against a traffic sign along a road. The letter T on the name “Toasties” was circled on the box, and the letter B was written above it with the letter K below.

The postcard sent to the station from “S Killett” bore the address of BTK’s first four victims, the Otero family, KAKE reported. It also indicated another possible BTK message — communication number seven — was dropped on Jan. 8. Landwehr also declined to elaborate about that message, other than to say police found it.

Police said they have received more than 5,000 tips from the public since BTK resurfaced.