They saw it in the distance, coming toward them, so surreal they weren’t even sure what it was. “For a minute we were like, ‘Is that a car?'” says Corey Lowe, 30, who was driving north with a friend on the Taconic State Parkway in Westchester County, N.Y. “It came speeding past us at like 80 mph. It was the eeriest thing I ever saw.” Behind them a 6-year-old boy in another car watched it go past and turned just in time to see the crash. “He said, ‘Mom, look, the car is flying!'” says his uncle Peter Dedvukaj. The boy’s mother, who saw the crash too, didn’t want him to be frightened and said, “No, it’s just a movie.”

If only that were so. The terrible truth is that on July 26 Diane Schuler, 36, put five children into her brother’s red minivan, drove it against traffic on the way home from a camping trip and crashed head-on into an SUV. Just like that, eight were dead: Schuler, her daughter Erin, 2, her nieces Emma, 8, Alyson, 7, and Kate, 5, and the passengers in the SUV, Michael Bastardi, 81, his son Guy, 49, and their friend Daniel Longo, 74. The only survivor was Schuler’s son Bryan, 5, left to be raised by his father, Daniel, who drove back from the trip separately.

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The deaths were an unbearable blow, but there was more shocking news to come: Toxicology tests showed Schuler had twice the legal limit of alcohol in her blood and had smoked marijuana shortly before the accident. “This is so out of the realm of possibility, it just blows my mind,” says Schuler’s best friend Christine Lipani, 47, one of several friends and relatives to insist to PEOPLE that the Diane they knew—devoted parent, virtual teetotaler—could never do something so reckless. “She was not an alcoholic,” Daniel Schuler, 37, said on Aug. 6 of his wife of seven years. “I never saw her drunk since the day I met her.”

Residents of the Long Island town of West Babylon, N.Y., where the Schulers live, plus newspaper columnists, bloggers and hosts of national morning shows have remained fixated on the tragedy’s central, unthinkable riddle: How could a mother driving her own children, and entrusted with her nieces, do such a thing? So far, despite tests, witnesses and family interviews, the mystery seems only to deepen. The toxicology results are clear. Schuler, a supervisor for Cablevision, had consumed the equivalent of 10 shots of vodka, and THC levels indicated she had smoked pot within 15 minutes to an hour before she died. (Tests also ruled out a stroke or aneurysm as a possible cause, though her family says Schuler had a painful tooth abscess and a lump in her leg that might have been factors.) “You’re either dealing with an incredible conspiracy, or the family is simply unaware of a drinking propensity,” says forensics expert Cyril Wecht. “The other possibility is that [the drinking] could have been a one-time thing for her.” Police found a broken bottle of Absolut vodka in the wreckage of the van and have evidence Schuler acted alarmingly in the hours before the crash (see box).

Still, none of this jibes with the portrait her loved ones paint of Schuler. Married to Daniel, a public-safety officer, in 2002, “Diane lived for the kids,” says Noreen Smyth, 38, a longtime family friend. She was also extremely close with her brother Warren Hance’s three sweet daughters: Emma, the natural leader; Alyson, the bubbly center of attention; and Kate, the baby of the group. What’s more, say family members, Diane barely drank at all. “I made the daiquiris at family parties, and if she tasted alcohol, she’d say, ‘Throw it out and try again,'” says brother-in-law Jimmy Schuler (the family does admit she sometimes smoked pot to help her sleep). One tabloid claimed she told a “drinking buddy” her marriage was troubled. Could marital problems have caused her to snap? Relatives and friends say no. “They were best friends,” says Jimmy. “And as long as I’ve known her, she never went to a bar.”

Schuler seemed fine when she pulled out of Hunter Lake Campground in New York’s Catskill Mountains—where the Schulers spent the weekend swimming and playing—at around 9:30 a.m. on July 26. “The kids were yelling out the window, saying they had fun and couldn’t wait to come back,” says the campground’s owner Ann Scott. But just hours later, Schuler’s niece Emma, talking on the phone with her father from inside the car, told him, “There’s something wrong with Aunt Diane!” At 1:30 p.m. Schuler drove up an exit ramp and into the fast lane of the Taconic. “She was not driving like someone who made a mistake,” says Corey Lowe, one of many motorists to note that Schuler “wasn’t swerving; she stayed in a straight line.” Several drivers managed to get out of Schuler’s way for two miles, but when she rounded a blind curve near Briarcliff Manor, N.Y., the SUV coming at her had no chance.

The crash was nightmarish. “People were running to the car screaming, ‘We need help, there are kids in there!'” says Dedvukaj, a Good Samaritan who pulled four children out of the crushed, smoldering minivan. Two of the girls were dead, says Dedvukaj. “There was nothing we could do. The third girl had a pulse, but she died later.” And young Bryan “was kicking. His eyes were closed, but he was kicking.” Dedvukaj also pulled Schuler’s mangled body away from the wreckage. “I was crying the whole time,” he says. “The kids weren’t moving. They weren’t breathing. They looked like angels.”

At Hunter Lake small toys and tiny flip-flops sat for days on the ground outside the family’s trailer. In the town of Floral Park on Long Island, where Schuler grew up, “everyone is holding their own children closer,” says one resident. And in a rehab center, Bryan recovers from his injuries (he has a broken arm, fractured foot and neck injuries). One night “Bryan woke up at 3 a.m.,” says his uncle Joe, “and he said, ‘I want my mommy.'”