Mary Fong Lau, 78, is arrested in connection to San Francisco bus stop crash that killed couple and toddler waiting on bus to go to the zoo

The driver who ran her SUV into a San Francisco bus stop and killed a couple and their toddler on their way to the zoo has been arrested. 

Mary Fong Lau, 78, was arrested Sunday on suspicion of vehicular manslaughter, driving the wrong way, driving at an unsafe speed and reckless driving. 

On Saturday, three family members, Diego, 40, Matilde, 38, and their one-year-old child died after Lau rammed her Mercedes SUV into the West Portal Muni bus stop. Friends identified the victims, but declined to reveal their last names. 

The couple's other child, an infant, was with them at the time of the fatal crash as the four of them waited to board the bus and head to the zoo. The baby is in critical condition following the horror crash. 

'A lot of things I know about love, I learned from them. They were an amazing couple. They had no issues with anything. It was love, love, love. They took care of the kids and were going to the zoo for a nice day at the park,' Rogerio Falerio, a close friend of the family, said. 

Some witnesses said Lau suffered a medical incident before the crash. Other said she got out of the car yelling 'What have I done?' Police have not released details on what led to the horror crash. 

Mary Fong Lau, 78, was arrested on Sunday after she slammed her SUV into the West Portal Muni bus stop in San Francisco and killed three family members. (pictured: A vigil that was set up Sunday at the location of the horrific incident)

Lau was initially taken to the hospital for injuries and it remains unclear what caused her car to hop the curb and crash into a fire hydrant, pole and side of the local library

 Three family members, Diego, 40, Matilde, 38, and their one-year-old child died after Lau rammed her Mercedes SUV into the West Portal Muni bus stop

Lau was initially taken to the hospital for injuries and it remains unclear what caused her car to hop the curb, crash into a fire hydrant, pole and side of the local library. 

Matilde was taken to the hospital after the crash, while her husband and child died at the scene. She died on Sunday in the hospital. 

Other people waiting for the bus to arrive were also injured from the crash and received medical attention.  

Friends of the family told CBS News the surviving child is about two-months-old and suffered life-threatening injuries. 

They lived in the Mission District, a neighborhood in the Bay Area, and planned to spend a day at the zoo together for Diego and Matilde's wedding anniversary, friends said. 

Falerio said that Diego was from Brazil and his wife was from Portugal. 

The crash site has since been covered with stuffed animals, flowers, candles, and a stroller with a heart-shaped cutout that reads: : 'Remembering the precious lives lost on March 16, 2024.'

Advocates from Walk San Francisco added three pairs of shoes in honor of the mother, father and child who were tragically lost. 

Witnesses said that the toddler went flying in the air from the impact of the crash. 

Another witness, Nikki Mashburn, told The San Francisco Chronicle that she heard the crash and that is sounded like 'an explosion.' She said that the victims suffered head injuries. 

'When the paramedics showed up, you could tell … they didn’t know what to do first,' Mashburn said. 

'The stroller was clearly destroyed. Yeah, so he was still strapped in there,' Johanna Dimayuga, a resident in the area told CBS News.   

Witnesses said that the toddler went flying in the air from the impact of the crash. Another witness, Nikki Mashburn, told The San Francisco Chronicle that she heard the crash and that is sounded like 'an explosion' 

The San Francisco Municipal Transportation Agency said Saturday it was investigating the cause of the crash in collaboration with the San Francisco Police Department 

Gabriel Cinquepalm, another witness, said that he saw Lau after the crash as she got out of her vehicle with a look as if to say: 'What have I done?' and that she was screaming at the sky. 

The San Francisco Municipal Transportation Agency said Saturday it was investigating the cause of the crash in collaboration with the San Francisco Police Department.

San Francisco Mayor London Breed said on X, formerly Twitter, that she had visited the scene of the collision on Saturday. She called it 'heartbreaking.'

Walk San Francisco has planned a memorial for the family at 5pm on Monday at the crash site. 

'We are heartbroken and heartsick and horrified,' Jodie Medeiros, the executive director of the advocacy group said.  

'This is one of the worst pedestrian tragedies to ever occur on San Francisco streets. It is almost beyond comprehension.' 

Following the tragedy, the group and locals have voiced their concerns about the intersection of Ulloa Street and West Portal Avenue where the bus stop is located. 

The group noted that around the intersection, there are multiple places where families and children frequent, like a library, schools and train stations. 

'It's time to fundamentally rethink areas like where this crash occurred, where thousands of people walk and cross and wait every day,' Medeiros said. 

This was the second child killed in the city in less than a year, as deadly crashes like these have surged and left residents uneasy.