The Orlando gunman had visited the Pulse nightclub and left before returning with an assault rifle and opening fire there, killing 49 people and injuring dozens of others, police said.
In addition, Mateen's wife -- Salman Noor -- has told investigators that before her husband left their Port St. Lucie, Florida, home that day for the two-hour drive to Orlando, she saw him with what looked like guns inside a bag and expressed "concern" that he was apparently leaving the house, as one source with knowledge of the investigation told ABC News.
Authorities have also determined that the day before the attack, three plane tickets were purchased online for Omar Mateen, his wife and their son to travel to San Francisco next month, according to the source. It's unclear who purchased the tickets.
These new details, first reported by CNN, came as Attorney General Loretta Lynch suggested there may be more than just one motivation behind the attack.
"Whenever you look at someone’s motivation or intent, whether living or whether they’re dead, you look at their actions and their activities surrounding the event," Lynch said today while visiting law enforcement and first responders in Orlando. "I cannot tell you definitely that we will ever narrow it down to one motivation. People often act out of more than one motivations, this was clearly an act of terror and an act of hate."
Lynch insisted the investigation is "active, it is open, it is ongoing," and she said authorities are still "working to identify anyone he had contact with that night, up to obviously and including any phone contact, any kind of electronic communication that he had."