Police were spotted going door-to-door asking Brian Laundrie's parents' neighbors if they had received a mysterious letter containing $20.

One neighbor said she received an anonymous letter with $20 affixed, instructing her to spend it to "feed the media and thank them." The neighbor, who did not want to be revealed, claimed the letters were sent to every house on the street, not just the Laundries' close neighbors.

Police asked neighbors to give over the letters and cash to North Port PD on Wednesday and sign a Property Receipt saying "suspicious incident," according to DailyMail.com.

Protesters storm Laundrie's home after Gabby Petito's autopsy released

Meanwhile, Brian Laundrie's father mowed his lawn beside a makeshift memorial for his fugitive son's late fiancée on Wednesday morning, 19 hours after a coroner determined Gabby Petito was strangled.

While being questioned by a reporter, Chris Laundrie, 62, was spotted with a grass cutter trimming blades near to the Petito monument set up in his front yard. Chris Laundrie dodged caution tape, bouquets of flowers, and photographs of Petito, 22, during Wednesday's gardening chore, while ignoring inquiries from an off-camera man.

Protesters also attempted to approach Chris and his wife Roberta at the Laundrie house in North Port yesterday night, banging on the door and demanding that the couple "speak out soon."

Gabby Petito's parents traveled to Wyoming three weeks after her body was discovered in Grand Teton National Park to retrieve her remains.

She died by manual strangulation, according to the Teton County coroner's office. Fox News reports that Petito's parents are planning to travel home to Long Island, New York, this weekend with her ashes.

After returning home alone on September 1 following a cross-country road trip with Gabby, the fugitive is the target of a major FBI manhunt.

Her parents reported her missing ten days later, and Laundrie went missing three days later. On September 19, Gabby's remains were recovered in a Wyoming forest, as per METRO.

Authorities suspect Laundrie is hiding out in the vast Carlton Reserve, where he told his parents he was going hiking on September 13, despite hundreds of reports and alleged sightings pointing to North Carolina's Appalachian Trail.

Despite the hunt, some Internet sleuths have resorted to a theory that Laundrie is hiding in his parents' garden flowerbeds.

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Brian Laundrie's family receives death threats

Since her fugitive brother, Brian Laundrie - the lone person of interest in the abduction and killing of his fiancée Gabby Petito - went missing, her family has allegedly received many death threats.

WFLA-TV claimed that Cassie Laundrie and her husband, James Luycx, had received threats of "killing his family and kidnapping his kids" as well as other "messages from strange people."

According to the news outlet, sheriff's officers visited Cassie Laundrie's house many times over the period of two weeks, the first time on September 19, two days after her parents reported her brother missing.

Following the threats, deputies visited the household on a daily basis. The family also reported "strange circumstances" at their house on October 1, which is roughly 40 miles from where Brian Laundrie resided with his parents and Petito in North Port.

Related Article: Coroner Reveals Gabby Petito Died By Strangulation 3-4 Weeks Before Body Found; Blogger's Mom Snaps Back at Brian Laundrie's Family