Pitt filed for joint physical custody on Friday
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Brad Pitt‘s filing for joint legal and physical custody of his six children with Angelina Jolie in response to her divorce filing (where she requested sole custody with visitation rights for Pitt) could result in a complicated battle, a legal expert tells PEOPLE.

Divorce attorney Christopher Melcher, who does not represent Pitt or Jolie, says Pitt’s filing a response on November 4 was really an expression of intent, and not a formal request for custody order, it does mean he’s not prepared to let Jolie have sole custody.

“[Angelina] checked a box for sole custody, he checked a box for joint custody,” Melcher says. “It’s basically just giving notice to the other party of what their intent is.”

Pitt’s filing in response to Jolie was also a move to show that he has received the divorce papers, and that he wants to participate in defending himself in the case.

But Melcher says it’s not a great sign for the ongoing divorce negotiations. He also admitted it is somewhat unusual in a case as high profile as this one, where the party filing for divorce usually gives the other an open-ended extension so they can work things out more quietly.

“It could mean is that settlement negotiations are maybe breaking down… or maybe she just insisted that he file a response [to the divorce],” he says. “If Brad is unhappy with the time Angelina is giving him with the kids, because she is really in control of that right now, then it’s on him to go to court and ask for a custody order.”

A source close to the situation has told PEOPLE that the children have been living with Jolie, and they are currently her sole focus.

“She’s cancelled everything else – work, everything,” the source said. “She’s been home each day, supporting them, helping them with homework, been there constantly. And no, this isn’t with a big staff of nannies and helpers.”

Meanwhile, the Los Angeles County Department of Children and Family Services continues to investigate the claim that Pitt was verbally and physically abusive toward one of their children in early September, and Pitt, 52, and Jolie, 41, are following the temporary family decision plan recommended to them.

(A legal source with knowledge of the situation has told PEOPLE that the DCFS are, “Looking for a history or pattern of behavior. They are looking at the original inciting incident and anything surrounding that, and looking at any relevant history,” while the family continues with therapy.)

WATCH THIS: Brad Pitt Files for Joint Physical Custody of Kids in Angelina Jolie Divorce Response

But for Jolie and Pitt to reach an agreement over custody, whether in court or not, Melcher says it all really boils down to rebuilding trust and communication between the former couple.

“You really can’t make an agreement without trust and communication,” he says. “I think what Brad is doing is wise because he seems to be following whatever DCFS recommended. He’s helping to restore trust, and then hopefully that will lead to communication, and then they can resolve this.”