Community members and activists are asking for urgent help in finding the man who fatally stabbed a Black teen and critically injured her sister in Oakland, Ca. late Sunday.

The horrific and gruesomely violent attack has shocked some on social media. Nia Wilson, an 18-year-old teen who attended Oakland High School, was fatally stabbed in the neck by an unnamed White man on a train at Bay Area Rapid Transit (BART) MacArthur Station about 9:45 p.m.

Malika Harris, Wilson’s sister, was also stabbed by the unknown man described as heavyset, in his 20s or 30s with short hair. He fled the scene and remained at-large on Monday.

While the motive for the crime is currently unclear, a police manhunt has remains underway.

MacArthur station had immediately been closed after the double stabbing and reopened Monday morning, the news outlet reported.

Wilson was remembered by family and friends who are pleading for help in finding the man responsible for the gruesome acts.