Investigators visited the North Port, Florida, home of Laundrie's parents, who cooperated with agents, Steve Bertolino said in a statement to NBC News.
"The FBI requested some personal items belonging to Brian Laundrie to assist them with DNA matching and Brian’s parents provided the FBI with what they could," he said.
Laundrie, 23, and Petito, 22, traveled across the country and documented their journey on Instagram with the #VanLife hashtag before he returned home without his fiancée.
He arrived in North Port on Sept. 1, police said. Petito's family reported her missing 10 days later.
Remains were found last Sunday at the Spread Creek Dispersed Camping Area in Bridger-Teton National Forest, near Grand Teton National Park in Wyoming. A Wyoming coroner confirmed that the remains were in fact those of Petito, and that the manner of death was homicide, the FBI announced Tuesday. The official cause of death will be determined when an autopsy is completed.
Laundrie is being sought by federal authorities in relation to a grand jury indictment for his "activities following the death of Gabrielle Petito," the FBI said Thursday. A federal court in Wyoming issued an arrest warrant for him Thursday, alleging that he "knowingly and with intent to defraud, used one or more unauthorized access devices, namely a Capitol One Bank debit card" and personal identification numbers for two accounts.
Laundrie hasn't been seen since Sept. 14, his family has told investigators.
While FBI agents were visiting Laundrie's parents in Florida, Petito's loved ones eulogized her at a funeral in Holbrook, New York, and fondly remembering her zest for life.
"When you leave here today, be inspired by what she brought to the table because the entire planet knows this woman's name now," the woman's father, Joseph Petito, told mourners.
"And she's inspired a lot of women and a lot of men to do what's best for them first," he said. "Put yourself first and do it now while you have the time. I couldn't be more proud as a father."