On the morning of March 23, 2012, Nicole Lei pulled up to her family’s home at 16 Howth St. The bright orange row house on a quiet Ingleside street is just a couple blocks from City College, and it was home to her mother Wan Yi Xu, father Hua Shun Lei, sister Ying Xue “Jess” Lei, brother Vincent Lei, and his wife, Chia Huei Chu.

It was a simple errand: Nicole’s 12-year-old daughter needed to pick something up before she went to school. She ran in while her mother waited in the car, only to emerge in a panic several minutes later. “Mommy, bodies, bodies,” she reportedly said.

When Nicole went inside to investigate, she found her brother lying in a pool of blood in the entryway. Her parents’ bodies were in the garage. Chu was in the in-law unit, and Jess was upstairs. Upon realizing all five were dead, Lei stumbled out onto the street, screaming.

The brutal quintuple murder shocked the city and stumped investigators, who spent days sifting through the house for evidence. The victims’ brutally battered bodies were covered in water, paint, bleach, and shampoo. Valuables, such as cameras and around $3,000 in cash, had not been taken.

But that afternoon, statements from two of Vincent’s friends, who had been with him the night before the homicides, led investigators to suspect one Binh Thai Luc as the assailant. Police tracked him down a day later, in the lobby of a Motel 8 in San Mateo, where he was reading about the murder on the internet. Now — more than five years later — he’s finally on trial for the crime.

In court on Tuesday morning, Luc bore little resemblance to the eerily gaunt suspect featured in a 2012 mugshot. He’s filled out, and was dressed tidily in a white collared shirt and gray vest. His neatly buzzed hair was gelled on top, and he wore thick glasses. He turned around in his seat several times during opening statements, scanning the half-empty courtroom, and appeared to be watching the door.

Prosecutor Eric Fleming from the District Attorney’s Office started his speech without any hesitation.

“He tried to hide evidence. He tried to conceal evidence. He tried to hide himself,” Fleming said, leading the jury in a gory blow-by-blow of the victims’ injuries. The details are ghastly: Autopsy reports show that each victim suffered skull fractures from strikes to the head and body with a weapon that is believed to be a hammer. A sharp weapon — possibly the claw end of the hammer — was also used. Jess was found with her teeth in her stomach. Vincent had been choked. Wan Yi Xu had a broken wrist.

Dimming the lights, Fleming walked the room through a photo tour of the house as investigators found it. While he described the scene in graphic detail, Fleming held back slightly with the images. Photos of the home did feature shots of bloody limbs and torsos, but faces were disguised or cropped out. He showed close-up images of blood smears on the walls, stairs, and floor. In particular, the prosecutor zoomed in on the sinks, which had been disassembled or stopped up in order for water to overflow and flood the scene — a move he implied someone with plumbing schools would know how to do. Luc, his defense attorney later revealed, was an experienced plumber.

And the evidence against him is damning. His blood was found in several spots at the crime scene, including inside a closed drawer, and his fingerprint was lifted off a bottle of Windex. After obtaining a warrant, investigators found a bloody pair of jeans at Luc’s home at 731 Haight St., which tested positive for Vincent’s DNA. Vincent’s blood was also found on the steering wheel and seatbelt buckle of Luc’s Mitsubishi car, and friends of Vincent had overheard him on the phone with Luc the night before the incident, planning to meet up. Fleming called it “devastating evidence of guilt,” adding that “He’s guilty beyond all reasonable doubt.”

Once the prosecutor had finished his eloquent tirade against the accused, the evidence was so stacked that it seemed as if the case was going to be over before it even started. But Mark Goldrosen, Luc’s defense attorney, expertly steered the jury into a world of doubt.

“He did not kill them, he did not help anyone kill them,” Goldrosen began. “Evidence will show he was present, but not that he was responsible.”

As he spoke, holes appeared in what had seemed a cut-and-dry case. There were, he points out, no eyewitnesses and no video footage to condemn his client — only circumstantial evidence, much of which does not link Luc to the crime. For example, two neighbors told police they heard a man yelling “Get down, get down!” outside the home at around 2 a.m. — in clear English. Luc, although fluent, speaks with a very distinct accent.

And after being apprehended by authorities, Luc’s body showed no signs that he’d viciously assaulted five adults: He was bereft of significant cuts and bruises. And near the bloody jeans in his home were shoes and a T-shirt that were both clean.

In addition, out of the more than 150 pieces of evidence collected from the home by police, only a handful were processed. DNA samples were taken from underneath the suspect and victims’ fingernails but never ran. Shoe prints were photographed and measured but never investigated. And, Goldrosen argues, other leads were never followed. A source reportedly informed an FBI agent that a local gang leader had ordered the family dead over a gambling or drug debt — a detail that was never investigated. “Keep an open mind,” Goldrosen pleaded with the jury.

And missing in all of this is a motive. As Goldrosen puts it, his client had a good life at the time of the incident. He was earning $45 an hour as a union plumber, and by March 2012, had already collected $19,000. He lived with his parents and brother and had a girlfriend. He and one of the victims, Vincent, were friends — and Luc was a regular at the family’s home, where they played mahjong for small stakes.

Thus far in the proceedings, no adequate motive has been raised that justifies the extreme violence of the quintuple homicide. But the case has just begun, and with a fiercely intelligent defense and prosecution — plus a plethora of evidence and a slew of witnesses prepared to take the stand — it will undoubtedly evolve in the days and weeks to come.