In a Los Angeles Times interview, John Kelly blamed Jeff Sessions for the family separation policy at the border.

Outgoing White House chief of staff John Kelly has pointed to former Attorney General Jeff Sessions as the person behind the administration's controversial policy of separating kids from their families at the border. 
In an interview with the Los Angeles Times, Kelly said: "What happened was Jeff Sessions, he was the one that instituted the zero-tolerance process on the border that resulted in both people being detained and the family separation. He surprised us." 
Though the responsibility of the program later seemed to fall largely on the shoulders of Homeland Security Secretary Kirstjen Nielsen, Sessions was, in fact, the one who announced the administration's new approach in May. 
"If you are smuggling a child then we will prosecute you, and that child will be separated from you as required by law," he said at the time. "If you don't like that, then don't smuggle children over our border." 
The policy was eventually ended by President Trump in June over intense backlash at the risks posed to the kids as well as the administration's poor handling of the families after separation occurred. 
Despite the outcry, officials have reportedly considered revisiting the program as a way to force families caught crossing the border illegally to choose either detention or separation while their cases are being processed.