Police announced a $32,000 reward for information leading to the arrest and conviction of the killer of Sandra Cantu, the 8-year-old California girl last seen skipping down the street near her mobile home, in a Friday afternoon press conference.

Tracy Police Sgt. Tony Sheneman told reporters investigators are making "good progress."

"We are confident we will be coming to closure sometime in the future," he said. However, he was unable to give any specifics except to say they continue to serve warrants.

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Earlier, investigators said they were narrowing their search but have been tight-lipped on details because they are getting closer to making an arrest in Sandra's killing, Sheneman told FOX San Francisco affiliate KTVU.

Authorities didn't want to tip off the suspect or suspects — who squeezed little Sandra's body into a suitcase and dumped it in a local pond — about the progress of their investigation by saying too much, according to Sheneman.

He has repeatedly told reporters in twice-daily news briefings that detectives are "moving in the right direction."

"We are still looking forward to a conclusion to this, but I cannot tell you what time," he said Thursday.

So far, investigators have interrogated Sandra Cantu's father, a relative of one of her neighbors who cops say kissed the child on the mouth two years ago, a Cantu neighbor and the pastor of a local church and his family.

Sandra was last seen March 27 on surveillance camera skipping away from the Orchard Estates Mobile Home Park in Tracy, where she lived.

Farm workers found her body in a suitcase at the bottom of a nearby pond on April 6 after an extensive search of the area.

Police have labeled her death a homicide. An autopsy is under way, but results haven't yet been released.

A police cadet also said Friday that he saw someone "acting real strange" at an irrigation pond near where Cantu's body was found.

The driver — a white man in his late 40s or early 50s wearing a white baseball cap and gray T-shirt — appeared to be looking down at the ditch beside the road, said 19-year-old Memory. Only four or five cars travel the remote road, which is a dead end, on a typical day, he noted.

Stephen Memory said he thought it was odd to see a beige Chevrolet Silverado truck parked on the shoulder of the road facing in the wrong direction on the afternoon of April 3. Sandra's body was found April 6.

Memory said he spoke to the FBI about what he saw.

On Thursday, detectives went back to the mobile home park where the girl resided after finding an envelope reading: "From Sandra, to my killer."

"You've taken my life away from me, but I forgive you and God will judge you at some point," the note inside said.

Sheneman said the envelope was found near a tree where a memorial of flowers, stuffed animals and cards was set up at the trailer park several days ago.

Investigators believe the note was left between 4 and 4:30 a.m. Thursday, but after analyzing its contents, they don't believe it is connected to the investigation, according to the sergeant.

He said such "false leads" slow, rather than help, the search for Sandra's killer, according to FOX affiliate KTVU.

Police have received 400 additional tips since Sandra's body was found in a suitcase Monday, according to Sheneman.

The 8-year-old's family broke their silence Wednesday for the first time since her body was found.

"We don't have any idea who could have done something this horrible to her," Cantu's aunt Angie Chavez said on the "Today" show.

On Thursday, the family issued a statement asking that no more items be left at Sandra's makeshift memorial because the sight is too painful for them. They asked instead for supporters' thoughts and prayers.

To date, police have served more than 15 search warrants in the case.

Click here for more on this story from KTVU.com.

FOXNews.com's Catherine Donaldson-Evans and The Associated Press contributed to this report.