Hunter Biden is aiming to limit evidence special counsel David Weiss can use in the case against the first son in Delaware related to allegations he illegally purchased a gun in 2018, according to court documents filed Tuesday.

Biden’s defense attorneys wrote that they plan to file “expeditiously” a request that Judge Maryellen Noreika prohibit Weiss from using evidence in the case that Weiss, in their view, “improperly gathered.”