"It was an honor to work with him, and I think that he'll always be in people's thoughts," Ledger's Brokeback Mountain costar Kate Mara, who played his older daughter, told PEOPLE at a Beverly Hills event for the Kenneth Cole Awareness Fund. "I think he affected people that he'd never met before."
In Australia, the Ledger family kept a low profile, and there were no notices in the local papers in memoriam.
"It's just a day-by-day thing," says a family source when asked how the Ledgers would be remembering the actor on his birthday. "That's all a private family matter. It's got nothing to do with anyone else."
A person called Karrakatta Cemetery in Perth, where the Ledgers have a family plot, wanting to lay flowers for Heath, but sources there tell PEOPLE that his ashes have not been interred.
Difficult to GraspA close friend of Ledger's from his hometown says the actor's death of an accidental overdose is still difficult to grasp. "I haven't come to terms with it," says the friend. "I'm just trying to get through it. It has really affected his friends."
And how is his father, Kim, holding up? "He doesn't want to talk about it," the friend tells PEOPLE. "He's a tough guy but he's a private man as well."
Also keeping a low profile was Michelle Williams and 2-year-old daughter Matilda. Williams has kept busy in Boston, working on the film Shutter Island, based on the book.
Meanwhile, the DEA investigation into how Ledger obtained the powerful and addictive painkillers 0xycontin and Vicodin will likely take several more weeks, a DEA source tells PEOPLE.
"Agents are still conducting interviews and are trying to get the proper documents to interview more of Ledger's doctors," the source says.
Reporting by MELENIE AMBROSE, MARIANNE BILKEY, SHRUTI DHALWALA and NICOLE WEISENSEE EGAN
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