Updated

Police are searching for a killer after discovering the body of who they believe is missing 18-year-old Kelsey Smith, who disappeared four days ago.

Members of a Texas-based search team found the body across state lines near Grandview, Mo., about 20 miles from where she was abducted.

"Pending completion of a forensics examination, we have reason to believe we have found Kelsey Smith," Overland Police Chief John Douglass said during a press conference Wednesday. "I promised them [the family] we will continue every effort to solve this case … and to bring her killer to justice."

But despite reports that said otherwise, Douglass said police do not have a firm suspect at this point. They are talking to several people regarding Smith's death, he said, but none are "persons of interest" or a "suspect."

"To be absolutely clear, we are talking to numerous people right now … but I’m not ready to identify any of them as our 'person of interest,'" Douglass said.

"The case is not over," he continued. "We still need the public’s cooperation to close this case and bring those responsible for Kelsey’s death to justice."

Douglass said police are still searching for a "person of interest" shown in a Target store surveillance video around the time Smith was abducted from that store's parking lot. They're also searching for a pickup truck in the area at that time.

"That person has not been locked down," Douglass said. "We’ve been looking at a lot of vehicles but we’re not convinced any of them are the one we’re looking for."

The murder investigation is now multi-jurisdictional, since Smith was abducted in Kansas but her body was found in Missouri.

Kelsey's family held an evening news conference in which her father described Kelsey as "scrubbed in sunshine."

"While the outcome is not what we hoped for, it did not lessen the effort of those out there helping," said Greg Smith. "The outpouring of ... help was a testament to how much Kelsey was loved."

FOX News learned earlier that police were focusing on a person who lives within two miles from where the body was found. That person apparently has a long criminal record. Police say they don't yet know the killer's motive but they do not believe Smith knew her abductor.

About 240 federal agents, police officers and police academy students were deployed to an area in south Kansas City — specifically, south and east of U.S. Route 71 and Missouri Route 150 — earlier Wednesday in search of Smith.

FBI Special Agent Jeff Lanza told FOX News that a signal from Smith's cell phone was last picked up in the area around 8 p.m. Saturday, roughly one hour after she was abducted. Investigators were conducting a grid search of the 900-acre area.

"Right now we’re just trying to follow up on all the investigative information we have to date," Lanza said. "It’s a needle in a haystack right now."

Searchers were walking shoulder-to-shoulder through the rough terrain of hills, brush and a lake looking for clues.

Overland Park Police spokesman Matt Bregel said earlier in the day the signal was a ping, which occurs whenever someone receives or sends a phone call. He said the ping in question likely was Smith's family trying to get hold of her.

"This is one of several angles we continue to explore in this case," Bregel said during a press conference. "We are still seeking the person of interest shown in the Target surveillance video, as well as the dark colored pickup truck which was also show in the surveillance video."

Bregel said police have received about 500 leads, 200 of which came in Tuesday night. But, he said, "just because we have received 500 leads, we are still asking to see everything ... we're following up on every lead."

Earlier in the day, Kansas authorities identified via video a dark-colored, mid-1970s model Chevrolet pickup truck as a possible vehicle used in her abduction.

Officials had released a surveillance video that showed a "person of interest" walking in close proximity to Smith while she was shopping, and being possibly the same person that was shown in a video rushing toward her car and forcing her inside.

Police still want to question the young, goateed man videotaped leaving the Target store moments before Smith's abduction. He has not been identified and was not being called a suspect, but he might have information about the disappearance of Smith, Overland Park Police Chief John Douglass said.

Smith's parents, Greg and Missy Smith, said Wednesday on "The Early Show" that they do not know the man in the surveillance video.

"None of our immediate family recognize him," Greg Smith told CBS.

Just before 7 p.m. Saturday, the pickup truck caught on video pulled into the parking lot aisle where Smith had parked about one minute earlier, police said. A man is seen leaving the pickup and going into the Target store Smith had entered.

Smith, who graduated from high school less than two weeks ago, left the store around 7:10 p.m. and put packages into her car when someone ran toward her, police said.

"You see two individuals come together, and there is no separation of those two individuals," Douglas said. "So it is easy to conclude there was some kind of incident at the back of the car. Then the car leaves."

But the tape was "just not detailed enough" and was being enhanced at a forensics lab, Douglas said.

"We see activity," Douglass said of the videotape. "We are moving on the assumption — because the prudent thing to do is to treat this as an abduction — that there was some kind of force involved."

More than 50 detectives and officers from the area, the FBI, Drug Enforcement Agency and others were involved in the case, he said. More than 500 people have volunteered to aid the search.

About two hours after Smith disappeared, her grandparents found her gray 1987 Buick in a parking lot at a mall in suburban Kansas City with her purse and packages still inside.

The Smith family had increased the reward to $30,000 for information leading to their daughter's safe return. Greg Smith, who has been in law enforcement for 16 years, described his daughter as an outgoing young woman who planned to be a veterinarian.

Click here to see photos of Kelsey Smith.

Anyone with any information that may help the investigation is encouraged to call the TIPS hotline at 816-474-8477 or the Overland Park Police at 913-327-5638.

FOX News' Alicia Acuna, Steph Watts and The Associated Press contributed to this report.