Thomas Matthew Crooks may have been struggling with an undiagnosed mental health disorder — including some form of depression — before he shot up Trump’s Pennsylvania rally, sources told The Post.

Although there are no explicit indications Crooks, 20, ever sought professional mental health treatment, his digital footprint uncovered by investigators so far includes internet searches for major depressive disorder.

It’s also believed Crooks fits the profile of a loner or outcast whose life has been characterized by isolation or rejection, with obsessive-compulsive tendencies and a knack for the mechanical or technical, including toward guns, sources said.

The investigation so far has shown Crooks had virtually no online presence, so authorities are focusing on poring over his electronic devices for answers to why he nearly assassinated former President Donald Trump at a rally in Butler, Pa. on Saturday.

But the search has been slow going due to the high volume of material authorities need to sift through — some 4.5 terabytes of data across a laptop, USB drives and two cell phones, sources said.

Searches of one of his phones haven’t revealed any clear motive for the young killer so far, but his web browser history revealed a broad interest in high-profile people, celebrities and politicians, regardless of their ideology.

In addition to doing searches about Trump and President Biden, Crooks also researched FBI Director Christopher Wray, Attorney General Merrick Garland, and a member of the British royal family, the New York Times reported, without specifying which royal it was.

Mayo Clinic defines major depressive disorder — more commonly known as depression — as “a mood disorder that causes a persistent feeling of sadness and loss of interest” and “affects how you feel, think and behave, and can lead to a variety of emotional and physical problems.”

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