US Attorney-General Loretta Lynch will meet with victims of the Orlando nightclub massacre.
The meeting on Tuesday (local time) comes a day after the Federal Bureau of Investigation said the gunman described himself as an "Islamic soldier" during the rampage.
Omar Mateen killed 49 people and wounded 53 others when he opened fire inside Pulse, a gay dance club, early on June 12 in the deadliest mass shooting in modern US history.
He was later killed by police after a three-hour standoff.
The 29-year-old US citizen of Afghan descent pledged allegiance to the leader of the Islamic State militant group in a 911 call from the nightclub, but authorities said he appears to have been "self-radicalised" and acted alone.
Citing unnamed law enforcement officials, CNN said on Tuesday that Mateen visited Pulse earlier on the night of his attack.
Reuters could not immediately confirm the report.
Lynch will be briefed on the investigation, the department said, and address the media alongside US Attorney A Lee Bentley III of the Middle District of Florida.
In a transcript of the gunman's calls released by the FBI on Monday, Mateen told police negotiators to tell the US government to stop bombing Syria and Iraq, and he threatened to strap bomb vests on hostages, though no explosives were found at the scene.
FBI Assistant Special Agent in Charge Ron Hopper told a news conference on Monday the shooter had made his "murderous statements" in a "chilling, calm and deliberate manner".