OAKLAND — Authorities allege a Pleasanton man urinated on a stack of Walmart purchases from his parents’ recent shopping trip, then used two 3D-printed handguns later that night to gun down his father in their shared home, according to court records filed Wednesday.

Alameda County prosecutors have charged Lucas Chan, 28, with murder in the fatal shooting of his father, Lance Chan, who later died at a hospital. The younger Chan also faces six additional counts tied to several suspected homemade bombs that investigators seized from his bedroom, among other charges, according to court documents.

The shooting brought a gruesome end to what authorities described in court papers as an otherwise ordinary day, which began with Chan’s parents going shopping at Walmart with another couple.

Lucas Chan told investigators that he became enraged Friday at seeing a vehicle belonging to his parents’ friends at the Chan household, because he claimed that one of those people had previously sexually assaulted him, according to the court documents.

While Lucas Chan’s parents and their friends were away at dinner that night, he walked out of his bedroom and — in an attempt at revenge — urinated on the bags of merchandise that his parents and their friends left behind at the house, the court records said. He then allegedly retreated back to his room, where he stayed until his parents and their friends returned to find their belongings soaking wet.

At around 9:30 p.m. Friday — sometime after his parents’ friends had left — Lucas Chan’s mother and father tried talking to him through his bedroom door, according to the court documents. When he didn’t respond, Lucas Chan’s mother walked to another part of the house.

According to what Lucas Chan told police, several minutes later he claimed his father said something along the lines of, “You wanted our attention, now you have it,” the court records showed. At that moment, Lucas Chan said he clutched a gun in each of his hands — both of which he had made from a personally owned 3D printed — and allegedly shot in the direction of his bedroom door, wounding his father on the other side, according to the court filings.

Lucas Chan then recalled hearing his mother’s cries as she tried helping her husband. He then called 911 and waited in his room for police to arrive, according to the court documents.

He told investigators that he had been unsure about who had been standing on the other side of his bedroom door. He had allegedly grown more reclusive over the past three to four years, to the point of cutting off communication with his parents. He rarely left his room, Lucas Chan’s mother later told police detectives.

The younger Chan remained held without bail Wednesday at Santa Rita Jail. He briefly appeared in court for an arraignment hearing Wednesday. He is set to enter a plea on Aug. 27.

Jakob Rodgers is a senior breaking news reporter. Call, text or send him an encrypted message via Signal at 510-390-2351, or email him at [email protected].