GILROY (CBS SF) — The family of Gilroy Garlic Festival mass shooter Santino William Legan said Tuesday they were finding it “impossible to reconcile this with the son we thought we knew.”

The FBI announced it was launching a domestic terrorism investigation of the shooting that claimed four lives, including Legan, and left 13 others wounded after discovering digital evidence that the gunman was “exploring violent ideologies.”

READ MORE: Marin County Focuses on Restarting Schools at Teacher Vaccination 'Super Pods'

“Our collection and review of the digital media in this case is ongoing, we are continuing to access data on several devices,” FBI Agent In Charge Of San Francisco Office John Bennett said. “We have uncovered evidence throughout the course of our investigation that the shooter was exploring violent ideologies. We have seen a fractured ideology. The shooter appeared to have an interest in varying, competing violent ideologies.”

Also discovered among Legan’s digital devices was a list of potential targets.

“The FBI and Gilroy police investigators have discovered a list of organizations that may have been potential targets of violence,” Bennett said. “These organizations from across the country include religious organizations, institutions, federal buildings, courthouses, political organizations of both major political parties and the Gilroy Garlic Festival.”

In their first public statement Legan’s family said they were “deeply shocked and horrified by the actions of our son.”

READ MORE: Berkeley Officials To Consider Making VP Harris' Childhood Home A Landmark

“To the families of Stephen Romero, Keyla Salazar, Trevor Irby, and to the injured that survived this tragedy, we cannot begin to describe our despair at his actions,” the statement read. “We want to express our deepest and sincerest apologies for the loss and pain that he has caused.”

They also were struggling to come to grips with the terror he brought to their hometown.

“We are heartbroken that he committed this violence in his hometown, at a family event meant to celebrate the tight knit community we have been a part of for twenty years,” the statement read.

Like others, Legan’s family is left to wonder why. The FBI said they still have not determined a motive.

MORE NEWS: SF Man Found Fatally Shot Early Saturday Near Oakland's Lake Merritt

“We have never and would never condone the hateful thoughts and ideologies that led to this event, and it is impossible to reconcile this with the son we thought we knew,” the statement read. “Our son is gone, and we will forever have unanswered questions as to how or why any of this has happened.”